knieman, what kind of league is it?
If it is an Open League, he is pitching against all the best hitters in history, so he won't end up with a 1.12 ERA.
But skunk206, one of THE most experienced and knowledgeable people here, is giving you good counsel: 4 games is a very small sample size. Any pitcher has 2-3 bad games in a row, even the very best. So 4 is well within probability.
If you are looking for leagues where having Bob Gibson 1968 means having the best pitcher in baseball, look for a Progressive League in an era you are interested in playing in.