He states in a later post that the bill is issued in the landlord's name.
Ah, missed that.
Definitely a gray area then, morally, IMO.
Tenant use electricity. Landlord buys electricity from the electric company at a negligibly-low rate that is obviously an error on someone's part. Tenant is not only fully aware of this, but intends to exploit it to its fullest.
Either the tenant is knowing buying a stolen service from the landlord (a crime), or the landlord messed something up somewhere and has that apartment's electric running through the wrong meter or something.