There are many public and private high schools that have a “first strike rule,” like it or not, even when what happens was unintended. It’s not worth arguing, as OP is dealing with her own particulars.
Caught with a vape may not concern the college as much as the hs. Presumably, with an early admit, everything else lined up well, LoRs presented a fine young man. But there’s too much we don’t know- including what level of college and how prepared he really is (will be) for college.