I believe he had acquired a lot of bitcoins already but in a silent manner, sometimes it's good to keep it as a secret so he can hide his true wealth.
We all know that he is one of the riches man in the world, but do you believe he declares everything he got?
I don't think a honest person like Bill Gates will hide his investment from the public. He probably don't need this investment because he doesn't trust crypto things. If he invests, we read this from newspapers
It could be said that you made my day for today
I guess no one should use the word "honest" in the same sentence with Bill Gates (if only as part of "dishonest"). As Steve Jobs (of which I am no fan either, just in case) describes Gates, "Bill is basically unimaginative and has never invented anything, which is why I think he's more comfortable now in philanthropy than technology. He just shamelessly ripped off other people's ideas". That's what Microsoft itself has been particularly good at, i.e. stealing ideas and then claiming them to be theirs since the early days of MS-DOS (or even before)