Haha, that's so typical. They start out side-eyeing your weird drink and then suddenly they're hooked. You must feel pretty good proving them wrong like that. Now you're stuck keeping him supplied forever, which is kind of funny. Honestly, it's a nice win when someone comes around to your homemade stuff.
Watching someone copy your thing never feels like a win to me. It starts cute but then they act like they discovered it. My roommate did this with my cold brew, went from calling it dirt water to making a whole show of "his" recipe for guests. Had to hide my good towels when he started using them as filters.