Its always important to try to look behind actions of ppl and who would benefit from those actions. If Elon simply wanted to invest in
BTCUSD he could have done so in silent. Tell no one. Just as you would not tell ppl everything, right? but then he announced it on twitter as he knows he gets big attention. the H4 candle was up 4k I think it was. Not sure but pjrice went up for a while after that Elon tweet. So yes he may have had something in the back of his mind.
He can't really make it silently because as soon as he does that he has to let people know on official papers, Tesla can't put 1.5 billion in bitcoin and only Elon knows about it, there needs to be a lot of people who know about it beforehand and also they put in paperwork to let shareholders and SEC and so forth know about it and obviously news hear about it and so forth.
He didn't tweet about buying 1.5 billion dollars worth of bitcoin as well, go check when it happened and his tweets before that and you will see that he only talked about it afterwards, he talked about doge a lot though, if they bought doge that would have been a bit risky. That is why I think Elon didn't really talked about it or tweeted about it to make more money after he bought it, he just likes it and just like you and me he wanted to talk about it, just because his company bought a lot doesn't change his rights to talk about something he wants.