"Obviously, he thinks your jokes aren't very funny! A position to which I can relate!"

Frankly, Ford isn't sure if he's angry with Horseriver or not. The guy snuck up on him and killed him, yes, but taking extreme measures to harm Bill Cipher is one of the many places where Ford's moral high ground is below sea level. He'd have to talk with the guy more to know for sure, find out what happened from a less Bill-biased point of view. But Bill absolutely deserves Ford's ire, in Ford's opinion. All this for a joke? He's death tolling, here!