Petnames can be chained. So if I follow some "John Doe" and give him the petname "John" and you give me the petname "Leo", then you could reference John Doe as Leo.John which might be somebody else than fiatjaf.john.

This can be extended for other stuff, too. Nips for example. fiatjaf.nip1 might or might not be the same as Leo.nip1.