Taking the armor of any guard was was troublesome, but it's still better then roaming around as a naked skeleton. But he picked the most conspicuous one to wear. He even noticed it's a mithril armor. "Too good to be left" I wouldn't be even mad at him, if he would just have packed if into a makeshift bag and run off with it. That magical GPS-Tracker really came out of nowhere and couldn't be anticipated, but it was foreseeable he would runn into trouble with the mithril armor set anyways. How much trouble and if it might be worth it would have depended on what he'd do with it:
- Sell it to a thieves guil for petty but pretty gold coin -> maybe not that much trouble
- Let it be reforged, to be unrecognizable -> the smith might rat him out, but it might have worked
- Wear it and show it off proudly -> Now that would have come around definitly to bite him
Yeah. It was stupid beyond believe.