So even though I know a single digit number of words, and you can count me in that two billion, nobody should care about getting it right on my behalf.
The people who can't read it, but who can see that it's broken, will form a lower opinion of your product. It's as if I went to a Polish website and the text was all right-aligned and in all caps. I can't read Polish at all, but I'd still form an opinion about the quality of the site.
If you screw up a language that has 0 readers, it matters far less.
The point of saying how many speakers there are was to increase the strength of that effect. Because of that, it's misleading if you pump up the number. For pumping it up to not matter, the number would have to not matter, and there wouldn't have been a reason to mention it in the first place.
Is it misleading? You don't have to be anything like fluent to realise when text rendering is broken. The quantity that is actually relevant to the discussion is the number of people who, when they look at your UI, will know that the arabic text rendering is broken; not the number of people who are fluent in arabic.