"buy"? You're an educated individual, aren't you? 🙄
Just because his girlfriend has her own mac app store account doesn't mean that they are violating the EULA by using her license to install on his macs as well. There is no way to determine if her mac is actually hers, or if his is actually his from the information given. She could be the administrator, and owner of all machines in question - so could he. If HE purchased lion on his girlfriends mac, that stands to reason that he is the system administrator and owner of the systems in question. This was never stated and can NOT be assumed, however.
Pay attention.