Berkshire Hathaway's market capitalization is more than $600B, so actually they could corner the market on it if they really wanted to (though it would probably become obvious that they were trying that long before it happened). They have no interest in Bitcoin because, from their previous comments on it, it produces nothing and they only invest in productive assets.
I think what the parent comment suggests is "Seal of approval" situation, similar thing that happened with Tesla buying bitcoin caused price surge. When a well known entity invests in crypto, trust in crypto goes up.
Berkshire buying bitcoin would definitely make me buy more bitcoin.
Exactly. But these guys are too old for the short game at this point. They are about legacy. And that should make these statements hit that much harder.