Elon Musk's main subject is Tesla and Spacex so I guess bitcoin isn't his business, right? Still this doesn't mean he wouldn't invest in it but 0.25? He says such numbers to gain attention of people cause they'll say: Oh such a rich guy and holds only 0.25 btc? Can you imagine? My neighbour holds more than Elon Musk and blablabla...
Personally I think that he owns much more, he is a type of a person who craves technological progress and probably he would save some of his fortune in Bitcoin because this way you are a little bit on another level in management of money. Btw I won't be even surprised if he offers bitcoin hardware wallets or will implement something similar in Tesla. Then he will be real supporter of it.