While I love Jae and his work ethic and his hustle, all NBA players have a little bit of diva in them. This could be very much about something in his personal life that he's being vague about. Not all athletes do this, but it's been known to happen in the past. I wouldn't read too much into it. Well know by Thursday whether those tweets have anything to do with trades. Hell the only person that should be concerned about trades is Bradley, since he seems to be in all these rumors. But he's not into using social media. Good on him.
AB likes to update his fans like many other athletes, the only reason he got rid of his page on IG is because groupies were being disrespectful and he had to tell them he has a g/f and child and to stop messaging him. He was off for a while but he has an IG page again (never had a Twitter page), he put it up maybe a couple months ago (can't remember), it's averybradleycamps. Before he was placed on all defense he had a pic up sorta lobbying for it and put up the tweet from CJ about him being the best p defender to thank him.
He use to post on his old account a fair amount, just a quick update on things and a pic here and there. He even changed his account name to spiderman0 (something like that) in the past, going by your logic we could infer that he is a bit cocky.
Like someone said above Jae IG/tweets like that all the time, he always says how blessed he is that the Celtics gave him his opportunity to show his game. Doesn't mean this isn't a cryptic tweet but it's not even remotely unusual for Jae's accounts.
Also, EVERY Celts player is on social media, some don't tweet/IG during the season much if at all and some are very active. The rookies at various times stayed off/didnt post much during the season but have started to do it again after the season, not sure if they were told to stop or w/e but they did.