Old School informed GURPS Dungeon Fantasy gaming. Basically killing owlbears and taking their stuff, but with 3d6.
Well this explains why my latest post suddenly got more views than normal ;-) I'm pleased that you noticed the hallmarks of your creation. I like them and have used them before in my previous DF game, but previously they have gone hungry. In this case the victim was "only" an NPC non-combatant, rather than a PC (because obviously easier target). I did some secret rolls to determine whether those on watch would detect the monster during the attack. If it had been spotted then the creature would have posed a greater level of threat for a ~62 point PC than for the default 250-pointer. From your description, I was expecting that the monster would likely run at the first shout of alarm or other sign that the caravan was mobilising, but your creation was sufficiently stealthy that the camp didn't find out until it was too late.
I think you ran it exactly right.I like to think of them as predators - so they'll try to corner prey, not look for a fight, and spook if threatened while hunting.