This should not be considered stealing. If you cause an enemy to drop their weapon, either with a disarming attack or spell, it's red so if you pick it up to stop them from picking it back up on their turn, it's considered stealing. If a neutral NPC is around, they call for help or turn hostile.
Just now in the Grand Mausoleum, I helped Nina Dortmel with her resurrection, and as I suspected, it didn't go well. I had Lae'zel use disarming attack on Garret, which succeeded, and then picked up his weapon. Nina then yells for help and several guards show up and turn hostile
I had to take a break from the game in April before the last patch came out, and I swear don't remember it being like this before.
