If I am Warren Buffet I would never made my acquisition secret since that is bad for my investment. I will use my influence to contribute to the growth of what I am venturing since somehow this will create huge profit for me. Also Buffet is smart investor so provably that those assumptions you have won't gonna happen since the guy seems want everything to be in favor on his side. But I think he won't go on Bitcoin anymore due to his age since maybe he know that he might be at lose if he invest with bitcoin at current situation.
But let see if there would be a change of thoughts and somehow see bitcoin as valuable asset also an investment.
After all, bitcoin is still a riskier investment than the ones he's making . So even if he had invested in it, making that investment public would not be a wise idea and would not benefit him in any way as you say, IMO. If bitcoin is dumped, his investment will suffer a serious loss, which directly affects his reputation . Not to mention , it will be difficult to avoid criticism or blame from those who invest from his advice.
We have no evidence to confirm that he does not invest in bitcoin, but given his position and reputation, it is completely understandable that he does not disclose it . It would be unwise to give investment advice on high-risk and volatile assets, especially when he is a well-known figure in the financial world. We are talking billions of dollars in investment, not thousands of dollars.