It's a business with huge fixed costs so they are forced to use dynamic pricing to cover those costs and maximize revenue. That includes "tricks" to get you to sign long term contracts and giving some people some deals versus others. His friend got the great price with the purpose of getting his friends to join the gym too. As for price discrimination being some evil thing--look at airlines when they sell their last seat for more versus an 30% filled plane. Or hotels auctioning last minute deals.

Relatively normal industrial behavior. The only thing that is shocking is that he's shocked.