It is relevant, because the memo was about the affirmative action like diversity programs at google. It was linked as evidence that you asked for, stating that google had such a program.
Affirmative action can work in 2 ways, either to solve clear discrimination by HR and hiring managers, or it will force an employer to lower standards of applicants to work towards a particular percentage of employees. I just find it hard to believe that out of 5000 managers, google would have that many who are chauvinistic. I would think those types would be a minority. Also submitting into evidence the fact that other silicon valley tech companies have to institute their own affirmative action diversity programs to try and lure women engineers, I would heavily lean towards not enough qualified female applicants as the cause of the shortage. In such a case, you would have to take less qualified female applicants over male applicants into order to hit target numbers.
Even if a minority of people in the hiring process are sexist, it could still have an effect on the hiring of women. If anything, being a large company with that many managers seems like it would
increase your odds that at least some of them are sexist. And given the many subjective aspects of the hiring process, it's entirely possible for subtle sexism to exist that would skew things against women.
There are other potential reasons a company could feel the need for affirmative action initiatives to lure female engineers. Maybe some women are shying away from silicon valley tech companies because of the reputation they have as being a boys club, or some other aspect that might make them seem less appealing for a woman to work there. In that case it wouldn't be the company lowering their standards to hire enough women to meet a quota, but trying to make themselves look appealing to skilled female employees who may otherwise look elsewhere. And we have no idea if Google even has quotas they're trying to meet, as your source doesn't contain any details on what form Google's affirmative action initiatives take.
So again, all you've established is that affirmative action programs exist (at Google and elsewhere), not what form they take or what effects they are having on the quality of people getting hired. Is it possible that this results in hiring less skilled employees at least some of the time? Yeah, absolutely. However, other possible explanations and outcomes exist. You haven't provided any substantial evidence that your explanation is the right one.
For the record, I'm not taking a stance on this lawsuit. I have no idea if it has merit or not.