Sure, people sometimes misuse the term ad hominem, but not in this case. The comment said that:

"Editorial articles in The Guardian are generally in sympathy with the middle-ground liberal to left-wing end of the political spectrum"

I fail to see how being liberal implies the bizarre views in the article. Bringing up the political leaning of the Guardian was a bit of a cheap shot and not at all germane to the topic.

"A critique is not ad-hominem if the target is a character trait relevant to the speaker's point."

As I interpret your sentence, that is not what the article you are quoting says, and it is also not correct. This is irrelevant here, however, because the character trait being discussed is not related to the speaker's point; it is merely an argumentum ad hominem.

How do you think that the character traits of the writer are relevant to his case against Google?

Claiming that the author was not objective is relevant to his argument.