I think people of his calibre are mostly thoughtful about what they convey to the public. Not everyone is like Elon Musk tweeting all day long what they think about Bitcoin. I can very well imagine that Tim Cook has been holding cryptocurrencies for quite a while, but would he necessarily decide very early on to make it public? I would rather not I guess, if I were him. Maybe he is trading cryptos like crazy, but would he make that information public? I really doubt it. By now he knows for certain that cryptos are here to stay and before politicians might decide for some moves against the digital revolution that he (now) has a stake in, he rather decides to raise his voice and let everyone know he has skin in the game.
Really difficult to tell whether he just recently bought cryptos or whether he is in it since 2012.