Friend Got Banned For No Reason.

so me and my friend urmomlololol was defeating the boss sayleros brother under the church. I snatched the drop ;) first. he got a little bit angry but he was fine. he said he will go kill the boss a second time. he gets the quest item and goes out of the church, on his way to Detlas. he was suddenly banned for using a cheat client. but last i checked. optifine is not a cheat client. this is true. we were laughing our ass off while this happened.
he tried to appeal it. but the admins thought he was dishonest and were not telling the truth. but he was. What should He do to get unbanned?

 

Are you sure that it was only optifine? Could you see what mods he had? What version of minecraft was he on?