I'm always surprised when a company is so quick to publicly comment on a sensitive personnel matter, but that said, it's interesting to note what this response
doesn't contain.
The OP basically called into question the quality and stability of Unbabel's platform ("The code was a tangled mess of mindless duplication, half-implemented features and misleading comments. Of the few automated tests that existed, most didn't even run anymore") and the competence of the people behind it ("The team lead was the only one who knew anything about the system and he was either busy trying to patch things up by himself or working with the other person they had hired for my position before I got there"). The subtle implication of the post: the OP may have been terminated because he recognized these things.
Are the OP's claims true? Who knows, but the response here doesn't directly address them at all. Instead, there's ambiguous language like "terrible fit", corporate-speak like "we believe that the culture of the company is extremely important" and a poorly-timed "A position just opened up :)"
Frankly, if I was the founder of a tech company and I made the decision to respond publicly to a situation like this, the claims about my platform and the competence of my team would be my focus and I'd address them head on. After all, such claims could become very harmful when encountered by prospective employees, customers and partners. Given that, it's curious they were completely ignored.