Unless we hear from account holders that their credentials weren't stolen, there's no reason to believe that only those were hacked that sent tweets.
Of course you're right that we don't know is if this is political, or just a distraction from whatever their real goal is / was. But the optics are clear here, and there is no reason to muddy the waters.
You can prove you have 'blackmail materials' just by proving you own the bitcoin wallet.
This looks more like data injection somewhere. Perhaps an old API exploit. You used to be able to send an SMS to tweet, for example.
(Went to wikipedia, but their suggestions like Death Metal and Dance marathon are probably not it ;) https://en.wikipedia.org/wiki/DM )