"You are not allowed to do that here." What does it mean?

I got to a fight with a "Crimsonite" Lumon and anything I try to do aside from forfeiting the fight gives me the message "You are not allowed to do that here."

https://imgur.com/ezRyH9s

Is this intended, or some sort of bug or softlock I stumbled into? Can I do anything to actually fight the thing? Thanks for any suggestions.