In other words, he was following standard practice for an unregulated crypto exchange.

Can I prove this? No --- the lack of insight and regulation makes it impossible to prove that it isn't.

If it's profitable and possible and no one is preventing it, the most reasonable assumption is that is occurring on a regular basis in the marketplace.

What would you do if you could predict large market influences with accuracy --- and you knew noone was watching --- or cared?

Rules for thee, not for me!