is this an instance of insider trading? how else do they pick these stocks up otherwise?
Potentially, but what do you think are the chances the SEC will come knocking on Birkshire's door? Rules for thee not for me apply here.
I would wager that the chances are not quite zero, but infinitesimally close.
It was already on a 25% discount because of the sexual harassment turmoil. A good value play without the acquisition. Berkshire thought so, and so did Microsoft later.