There’s no harm in being suspicious. Worst case is that you’re wrong. Best outcome is that you were right and the bike & owner get reunited and some scumbag gets a firm telling off by the police!
If you go back to the house & the bike is there,see if you can get the frame number. Just dont get caught looking!
If you can, you can check to see if it’s reported stolen on bikeregister or a few other sites that track numbers. Just Google them.
If you get no results, at least you tried.
I’d love to check a few bikes I’ve seen some teenage hoodies sneaking about on. They definitely don’t look like they own them. I’d have to push them off first which kinda gives them a hint somethings up!!