Yup. The stats stay the same throughout the rest of the day making the thievery check later on pretty easy. I tried it on an entirely new playthrough and got a similiar increase that put me over 100
I see what it is. All the other skills use a mix of attributes and karma to set their levels. Thievery uses fitness though. It looks like I just had a massive brain fart as it is originally set to body but during level up uses fitness. Thus if you have a high fitness it gives a big boost to thievery. I've fixed it now so going forward it'll be correct.