This top one player is wearing a dagger and a hand crossbow. How is it possible ? When I try to wear both of them I have the message that I can't equip a hand crossbow in my off hand slot if I have a dagger.
This is a bug, and is fixed now. The guy on leaderboards did climb there before the fix, and now no one can catch up with him, probably.
The bug was that you could equip a Hand Crossbow if you already held a broken Dagger - the game checked that the hero is not using a dagger and then allowed the crossbow. Then, of course, you just repair your items and voila.
Btw, guy's nickname means "Piglet's gun" :-)