I do not know for sure what the law of the land is
If the a/c is not on and pumping air out then it is an open pathway.
Besides mine whose air runs constantly? just my 2 cents but I likely would not have even thought of it at the time, especially since my garage is just storage. I would definitely mention it but if it is NEVER used for vehicles or turned into an office I would likely “verbally” tell the client no problem. I would likely write it up as a defect to cover my a s s. I say good thought and catch.