What did i just do to my boyfriend?! (TMI)

He and i were in his car and i was jacking him off, and i moved my hand somewhat under his dick towards his left leg, and i wasn't on his balls or dick but he like FREAKED and like started like really moaning a whole lot and he arched his back and he started breathing super hard but he wasnt cumming. but whatever i did i've never done before and he has no idea what i even did or what he was experiencing or feeling and does anyone know? we're both so confused, neither of us have experienced that before. but it was really good for him so i guess it's good lol