Yes, partner kicked off by dealing and passing, then bid all by himself to the 5-level.
RHO is a very very very random pre-emptor (so far in the match he has opened at the 3-level on Kxxxxx with an AK outside in second seat at love all, and QJ10xxx with a queen outside in first seat at game all).
4♦ on your left was slow
5♣ on your left was very fast
Now what?

Help

P 3♦ P 4♦
4♠ P P 5♣
5♥ P ?