No, he talks about both:
> I’m simply stating that the distribution of preferences and abilities of men and women differ in part due to biological causes and that these differences may explain why we don’t see equal representation of women in tech and leadership.
and
> These two differences in part explain why women relatively prefer jobs in social or artistic areas.
(emphasis mine in both cases). And that linked document does support that claim of his.
(Again, I'm not defending all his claims; just that one.)
I think it's because he wants to write sentences like that one about "preferences and abilities" in an attempt to pretend that arguments about preferences translate to arguments about abilities.
That is, I would have agreed with a claim that he has two distinct theses (preferences and abilities), except that the actual purpose of the essay is indisputably about abilities, and there's no reason to also add a thesis about preferences other than to muddy the discussion about abilities. A similar essay about preferences alone wouldn't have drawn nearly as much attention because it wouldn't be suggesting that the women already at Google shouldn't be there and it wouldn't be relevant to the Google D&I programs he mentions.
If preferences partially explain why psychology is dominated by women and why computer science is dominated by men, then preferences can partially explain part of why psychologists tend to be women and tech employees tend to be men.
And that's a big part of the memo: why is there a gender gap, what causes it, etc. So it's not surprising that one issue he focuses on is preferences. And he's not alone in doing so, that preferences are important in the tech gender gap discussion is something agreed upon by both sides:
* A lot of important diversity work done by progressives focuses on increasing interest in tech among young girls: girls' preferences matter.
* And on the other side, conservatives tend to say that preferences explain most of the tech gender gap and not discrimination.
I am disputing that preferences are relevant to the business purpose of this memo, which was to claim that what Google does with applicants once they have applied is both unlikely to work and illegal.
I am also disputing, more directly, that he or anyone has shown that preferences are relevant to the gender gap for engineering roles at Google; I'd think that there exist both more qualified men and more qualified who are interested in working at Google than Google has positions for, and the difficulty is in identifying these people. This is supported by how the specific diversity initiatives that the author calls out are all about properly evaluating applicants, and none are about encouraging people to apply or have an interest in the field. (And anecdotally, as someone who received a job offer from Google in May and spent three months going through team selection and ended up accepting another offer, both my own experience and the stories of others I've talked to both inside and outside Google is that headcount is sparse.)
These two claims I'm making (that preferences are irrelevant, and that the memo does not argue that preferences are relevant) are definitely falsifiable, so I'm interested in evidence to the contrary.
Note that this is a different point from the gender gap in tech as a whole. I'd definitely believe that preferences are much more relevant there, especially if we count things like wanting better work/life balance (or wanting better maternity leave, etc.) as preferences.
Clearly both are important topics, and they have some obvious connections - for example, the gender gap as a whole often motivates specific corporate policies, that's one reason he brings it up - but they can also be debated separately.
So I think it's fair to say the memo does make some valid points, but it looks like you think it's wrong on other points that it makes in other areas (which could well be true).
I just reread the document to confirm I read it right the first time. The subtle implication, and I'd argue one of the most harmful effects of the document, is the claim that biases (whether from nature or nurture) in interest also translate to biases in ability. There's a huge difference between saying "More men than women are interested in the job but we've got to hire the most qualified people regardless of either gender or interest" (and he almost gets there in his discussion of men seeking high-status jobs!), which I don't think I could really complain about, and "More men than women are interested in the job so our efforts to hire women are 'effectively lowering the bar' and probably illegal."
If you are at the point where you have 10 resumes on your desk from 10 qualified women, and 10 resumes on your desk from 10 qualified men, and you put together a team of 9 men and one woman, no matter how true it is that women as a whole are less interested in the job, it's not relevant.
(Incidentally, that's a quote from the portion of the abstract where they're mentioning existing research instead of their own, and it cites three sources, the first of which is a book by a lawyer that appears to be targeted at the general non-fiction market. I'm rather surprised that this is a permissible citation in a scientific paper, and I'm wondering if my standards are wrong or this isn't a super reputable journal.)