PC Overheated during update?

So this is an odd one. This current PC I built maybe 8 months ago. I haven't had any issues with overheating ever once I got my fan curves all set good in the very beginning. Just today I was gaming and again nothing seemed off. I finished up and did update and shutdown. As it was updating I walked away as I usually do. (I'll never do that again) I come back about an hour later and my room smells like something is burning and it's noticeably warmer in the room. I don't know what happened but it's like my pc shut off but the motherboard and cpu were still running. All my fans were off. My AIO was off. Everything except the motherboard and cpu. The PC was sooo damn hot I could barely touch it. I killed the power supply and unplugged it immediately. Opened the PC right up and got a fan on it. Once it cooled down I bravely powered it back up and it seemed to be working with no issues. But now I'm skeptical. Something had to have gotten damaged. It was HOT!!! burning to the touch hot. With out a single doubt in my mind it was hotter than a thermal shutdown under "normal" conditions. Way hotter.

Long story short though. What the hell could cause this to happen. I've never seen this before.

Although it seems fine. Is there anything I should do just out of precaution before I start using it again. Such as re-apply new thermal paste possibly? Should I change the CPU power cable? And of course I'll never just walk away again. I'm even gonna kill the PSU switch going forward.