User blog comment:FairyRaven/Fairy Tail Chapter 429 & 430: Code Blue & Purification Ritual, Review and Commentary/@comment-5006572-20150420142523/@comment-24038953-20150420145911

It is possible that Frosch would have run to Gray for protection when Rogue started fighting and Gray was still acting as his undercover self. This could have led to him being mean to Frosch and causing him to run away crying, and he ran into the battle and was killed. Future Rogue would have blamed Gray specifically since he caused Frosch to run.