Unless you are Superman everyone has an off day now and again. Nothing to be ashamed of and certainly not after riding 100 miles.

When I used to play a lot of competitive sport there were some matches where for some reason I just couldn't perform as normal - no energy. Could never explain it, just had to go for the next game

Sounds like your job(s) give you a lot of stress and little free time. I think you're doing great just to be disappointed at feeling pooped after 100 miles.

Keep on riding and enjoying that Californian weather, and don't beat yourself up about it.