He's drunk. Upset. Tired. Smoking.

He wanders the neighborhood closest to the bar he was at, just looking around.

He saw your house, the biggest one there. Out of curiosity of the light turned on at 1 in the morning...

He comes over, stumbling down the ditch to get to the window. He'd never seen this before.....well, he'd never been there before.

After looking in for a bit...he knocks. Scaring the crap out of you.