I hate to break this to you, but we’re just simple carbon based life forms, and everything that feels good “works by hijacking your internal reward system.”

This isn't a "gotcha". That's the premise of their point.

I think what they're pointing at is that this system can be taken advantage of in ways that are negative (e.g. addiction). A lot of games, especially ones monetized around micro-transactions, are designed specifically to exploit people's "reward system".