Once again, nothing there implies that they were chosen solely because they were friends. Could have been highly qualified people who just happen to also be his friends.
Not surprising since BoDs are drawn from surpassingly small and tightly-intertwined groups -- though every market and market vertical tend to have their own sets. Everybody knows everyone in those worlds....
The interesting question then really is: how exactly do you staff a Board of Directors? Not a question that a lot of people struggle with, I'm sure. But perhaps something that needs a better answer than "with the people I know and trust".
EDIT: s/one/some/; s/a close friend/close friends/