Was he rummaging through bins?
no and that's what made us notice him.
Absolutely it is potentially suspicious. Are you not aware that burglars target houses with for sale signs? And what can be seen from a window? Nothing, that's what. Anyone who likes a house from the curb needs to jot down the number and arrange a viewing. Period. You cannot judge the interior by peering into a single window.
You're right that there is no crime and no law broken, but I sure as hell would want to have neighbors who call the cops about anyone looking into my windows while I am not home. So absolutely the cops should be called and they should check the guy out. Dylan understood their reasons for their actions, why can't you?
If the house is empty, WTF are they going to steal?