This is a case of a famous, high status person making a statement without credible arguments. In other words, if a non-famous person said this, nobody would take him seriously (or noteworthy), because he doesn't really contribute anything to the discussion about bitcoin. The internet is full of good comments about bitcoin (for and against), but more visibility is given to Buffet's comments because of his status.

I guess media is to be blamed here to some degree. If someone is famous, then the media will make a story about anything that increases ad revenue. And also users of social media like Hacker News.