Reading this, I do get the impression that the Partially Meets Expectation was given to get more work out of this guy. It's the worst kind of manipulation - spinning something that was an unqualified success into a "failure." Especially because the boss clearly already had an internal narrative, and it sounds like they cherry-picked feedback from coworkers to support that narrative.

Having had something somewhat similar happen in the past, it seems like this is common at high-growth tech companies. Everyone pretends to be your friend, and there are definitely some genuine people, but getting ahead is clearly number 1.