1st Time Watcher question

Enjoying the show so far, only halfway into episode 2 of season 1, and had a question. Matthew has been around her constantly for at least 2 days now with a vampire's enhanced senses, but he has to press her jacket to his face before her scent triggers his "craving"? I tried looking through past posts but didn't find an answer. Maybe it's not a big deal? Am I making it one? It's just so curious to me and I can't seem to move on lol