The things you think sap his credibility add to his credibility for me; if he was making things up, it would have been easy for him to leave his own politics and sensitivities out of the post to make it more painful for his ex-employer. To me, it reads like he's just venting to his peers. We're the ones making a big deal out of it.
Yes: if his "plan" was to defame an employer, he'd want to conceal his views (which, again, are completely irrelevant here) as opposed to express them in a transparent fashion (which he does).
Finally, you have to wonder, how much of abuse the employer had to dish out to turn (judging from the picture) an apolitical gamer-hipster-nerd into an anti-colonial radical. I don't want to make this story about me, but as a secular
Jew who immigrated from former USSR as a teen, I can say that experiencing racism firsthand tends to change your perspective.
People who want to discredit somebody will use any convenient tactic. A decade ago, I bet you'd hear users citing the author's substance abuse problems and resulting instability because he admits to lighting up after work.
Yeah, just as long as that sort of shit isn't in his official complaint, it's not really an issue that he's peeved about it. But that's the sort of thing that a lawyer would seize upon to try and demonstrate that someone has a distorted perspective.
If I were his editor, I'd tell him to separate the, "Dumb white hipsters being ignorant", stuff from the, "Creating a hostile working environment", part of his story. As it is, it's mixed in and undermines the seriousness of the legitimately awful treatment he was subjected to.
In this situation perhaps it's most constructive to proceed with the conversation under the assumption that he honestly related his experiences, while acknowledging that we don't have a solid reason for believing him. We could run around in circles all day trying to reason things out -- for example, I could point out that exaggeration and embellishment are normal when people vent to their peers -- but we'd never get any closer to the truth. Unless we know him or the people he's talking about, we can't evaluate his credibility without making some unjustified assumption (such as the assumption that he's worse at lying than you are at spotting a lie,) but we can justify treating the story as honest on the grounds that it leads to a more interesting conversation than treating it as a lie.