Perhaps the author’s approach would lead to less gender diversity at the company if it were adopted. To shorthand his position as “anti-diversity” before the fact is still misleading.
Journalists grasp this nuance on lots of other issues.
Donald Trump campaigned on the promise of more jobs for working-class Americans. In service of that end, he has proposed canceling free-trade agreements, building a wall to keep out immigrants, and eliminating lots of environmental regulations. Critics who avow that they favor more jobs for the working class, but oppose achieving more jobs through those specific means, are not described as “anti-job,” especially when they suggest specific alternatives for job-creation. Even if their alternatives would result in fewer jobs than the Trump administration’s plans, that still wouldn’t make a writeup of their proposal “an anti-job memo.”
To object to a means of achieving x is not to be anti-x.
The failure to apply that same logic to the author of the memo is straightforwardly frustrating for those who agree with many of the views that the memo expressed.
The key to this reasoning, though, is that the journalists in question must not have any other good reason for having labeled it "anti-diversity".