So your red tail was getting beat up, which is stressful for the little guy. Then you move him to another tank to be away from the gar, good move, but moving tanks can also be stressful for fish. So he's got stressed from two issues, the bullying and the moving. RTC's are renowned for regurgitating their stomach contents when stressed.
I'd let him settle in his new tank with lights off for a while. Maybe add some salt to help with his injury and don't try and force the feeding issue, he'll eat when ready.
Most important, keep that water clean and stable parameter wise to prevent stressing him even more.