True, I wasn't precise enough. I was referring to the earlier comment "Buffett has always said he purposely avoids most of them because he doesn't understand them well enough.", so I mean the has no opinion on most of them, and avoids them (neither buying them nor shorting them).
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.
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...