Anytime someone is at a company for less than a year and "departs," rightly or wrongly I assume there was some lack of meeting of the minds. I've known professional friends in that position but never asked about details.

The only thing that might give me pause is that there's no conciliatory language coming from Mongodb to indicate that it was a negotiated exit, not even a bland "by mutual agreement".

In fact, they seem to have gone out of their way to minimise any mention of him which, to me, suggests that it might have been worded that way based on legal advice rather than for PR reasons.