Could that have to do with them ounishing wrongdoers by making them spore zombies? I'm sorry it ended that way. Tbh though, I won't risk pickpocketing in HM. It is so easy to just aggro everyone. If that happens in the grove or in LLI, you just loose all the refugees and harpers (plus someone had the bug tha tRaphael got aggroed too and just did sent his 899 hitpoint ass into the fighting).
In BG I think, all steelwatchers can be aggroed, if you are unlucky.