Yeah, it seems sometimes someone just magically senses that you've stolen from them, and while you never incur a bounty, they still hire some thugs to hunt you down. In my case I stole some ingots off the porch of the blacksmith in Riverwood in the dead of night, with nobody watching, and later met a group of heavily armed and armored mercenaries near Whiterun who had been hired by him to 'teach me a lesson' for it.. They didn't kill me, but they were the most powerful humanoids I had fought up to that point. To be fair, theft is otherwise a bit OP and too easy to get away with, but psychic property owners hiring seasoned veterans on the cheap is a bit jarring to the realism factor.
