I think they confused "slur" with "swear" and are referring to the f-bomb on the last page. It might have set off some alarms as a previous translator had a penchant for having Ikezawa swear every other page (notably calling Eguchi "that cunt") regardless of contextual suitability and responded to criticism by claiming that's how English-speaking teenaged boys talk casually in Britain. It was a whole thing.