@fesshole Likely it's just in case he loses his original key. That way he can show up and ask you for it back so he can get into his home if he loses his key on holiday.
@fesshole An interesting, and not quite ridiculous, approach to his #security. If the emergency arises he'll send someone to collect the #key. Until then you don't know where his house is, and someone doesn't know where the key is. And a general call of "who has a key for ..." doesn't work well either. The two of you are factors in a forward-anonymous key management system, I think.