It's possible the author is experiencing cognitive dissonance, but you should consider that maybe they've thought about the issue for a while, and come to conclusion that working at Facebook really is the best to achieve the goals they care about. They've worked on Tea With Strangers for 6 years, so I think it's very unlikely they haven't thought about this consciously, and just "deluding themselves", as another commentator suggests.

Now, I'm guessing that it's an obvious conclusion to you that working at Facebook goes against the goals the author suggests, and hence you dismissed it as cognitive dissonance fairly quickly. So then question becomes, why is obvious to you while not to the author? My suggestion is the author is starting from a different set of axioms than you are, which leads to a different conclusion.

I was able to come up with multiple axiom sets[0] that allow coming to the conclusion that working at Facebook is a positive way to achieve the author's goal, within about 5 minutes of thinking, so I think your conclusion is far from obvious.

[0] - I don't necessarily agree with most (or any) of these. My point is more that these sets do exist.