- I don't understand thing ABC, therefore I won't form an opinion on it (true fact, by his own admission... conservative and reasonable).
- Thing XYZ is generally acknowledged to be more complex and harder to understand than ABC (debatable, but I'd love to see someone show me how crypto is easier to understand than Google/Facebook/Amazon/Uber/etc.).
- Even though I don't understand ABC and won't form an opinion on it, I will form an opinion on XYZ which I understand even less (... wut? Why would anyone put stock in this statement, given the prior two statements?).
He is a major investor in Apple and was a relatively-early backer of BYD, the Chinese battery technology company.
[1] https://www.cnbc.com/2017/02/27/billionaire-warren-buffett-m...
[2] http://money.cnn.com/2017/10/11/investing/byd-warren-buffett...
That goes to show that he's aware of the limits of his expertise, and clearly he has an opinion on bitcoin, so presumably he considers them within his range of expertise.