Your friend the renter has exclusive control over his apartment, with minor exceptions for the maintenance thereof. He is the person who can authorize someone else to enter. The landlord, outside of fairly narrow exceptions for maintaining the property (often subject to prior notice to the tenant except in emergencies), cannot do so. The no-sharing policy is unenforceable because it is invalid; the renter has the right to loan a key to someone (yes, even if subletting is prohibited, he can legally loan his key to someone else, e.g. for petsitting).
The differentiation is: who controls access? In this case, the company owned the computers, and the dude accessing them did not have permission to access them. I'm not a fan of the way CFAA is used, but this is a pretty clear violation.