It's quite simple, really. I used to be like yourself, but then I read the famous How to Win Friends and Influence People. Dale Carnegie wrote it in the 1930s, which explains the weird title, but don't shy away from it because of that. It's actually very enlightening!
Correct me if I'm wrong, but isn't it bad for him to talk about this publicly and insinuate that his manager was shit and that he was fired for no good reason?
This situation reminds me a lot of the time an ex-employee of reddit complained about his firing, on reddit (!!), and was publicly called out for it by reddit's CEO at the time [1].