My new kitten balding patch from eye to ear?

We got a kitten just a few days ago and ever since we got it i noticed he has a slight patch balding out about 1cm wide and from the side of his eye up to his ear diagonally. i did some research and it said that sometimes this is completely natural and happens genetically sometimes, but also it could be some bacteria eating away at his face? the vet said there was nothing wrong with him but since he came from an adoption shelter maybe he got it from some cats there? Should I wait and see if hair grows back and will it grow back shortly or should I go to the vet soon? The kitten is only 4 months old.

Is the kitten black?  That is common to look like fur is thinner running on an angle from eye to ears on a black kitten. They even talk about the angle to take pictures of black kittens so that area does not show up on film. My cats grew out of it as they aged.