Richter clearly threw the door open and marched in with his goon squad trying to store up trouble. He may not have done the actual insulting, but those are his people and their words/actions are probably indicative of what they’re usually like.
The fact that Richter has a goon squad wandering around the castle means he’s probably important on some level. And in a class-structured society (on multiple levels, both jobs and noble ranking), the bottom-tier MC is probably used to having to acquiesce to the demands of others. Thus, he answers their question without thinking, because he’s conditioned to do so in order to avoid more trouble. On one hand, the MC doesn’t want his actions to reflect poorly on his new benefactor; but once Richter’s goons direct their insults toward said benefactor, all bets are off.
Meanwhile, I’m sure Krona knows exactly who Richter is, and is stepping in before the MC gets himself into trouble. It probably also means that she’s come to expect this kind of behavior from both Richter and his entourage, thus she holds him—their ringleader—responsible and gives him a mop to the face.