That only refers to Major events. Once you take cash in a Pro division you can not play Major Am events. So no Pro Am Worlds basically. Other than that, as long as your rating is low enough, you can play all the Am events you want.
An Amateur player is automatically re-classified as Professional when the player has accepted cash while competing in a Professional division. Accepting prizes in lieu of cash payout or accepting money for winning an ancillary contest such as an ace pool, top-of-the-card round prize, or CTP contest does not cause a player to relinquish his or her amateur status.
As far as Tom and that $40 in Pro goes, you'd have to ask him if he accepted cash or prizes there. I'd hazard to guess it was prizes as he is quite aware of the rules around Pro vs Am classification.
You may not Play in AM Majors as a "Pro Playing as AM" per http://www.pdga.com/files/2014%20PDGA%20Tour%20Standards.pdf