This would be creepy even if he wasn't a cop. If I knew a girl from somewhere, say class or something, and looked up her address online to leave a note without already knowing her decently well, it would be creepy as hell. It's just the whole "you don't really know me but I know where you sleep" aspect that's screwy.
Plus, the dude met her in a situation that could very well imply abuse of power. He could have pulled her over just to force a meeting or something to that effect. From the details given in the note, he seems like just a nice guy who made a stupid decision and I'm not saying he DID pull any bullshit like that. But the fact remains that he made one creepy gesture and it opens the door to speculation. It's just uncomfortable to think that someone with the authority of an officer could be a little bit deranged.
But like I said, IMHO he just sounds like a nice guy who did something silly without thinking it through. Just blind-contacting someone like that always runs the risk of coming off as creepy, but he could have just looked up a phone number online and made a call while seeming about half as stalkery lol.