As long as he didn't place any bets, I think what he did is totally fine.

If I find out my friends placed bets on whether I'll say X tomorrow, I'm not obligated to act as if I didn't know.

So is it also okay if his friends placed a bet and shared the profits with them?

Don't quibble on details. The point is that as long as he didn't profit from the bets, he is free to mess around that way.

This isn't share price manipulation.