Maybe the Valentine's chocolates are tied into the trophy for seeing all of the affection scenes?
How do you mean? The main way to receive the gifts is through the girls actually handing you them, though you can get them from training. Still, I've seen every one of them hand me a gift and didn't get a trophy.
Unless you're referring to some other scene?
I guess you're referring to the scene after you get them to five hearts. I can't really imagine why they'd make the Valentine's Day gifts be related to those, since they already take a good deal of time for anyone not
speedrunning the game. If one did get all the scenes before getting all idols to five hearts, it'd seem like a coincidence, anyway.