In the final scene with Chuy, Brando weaves his leather poncho belt with his hat band, to lasso his rifle. When the shooting is finished and he stands up, the belt is back on his poncho, although there was no time to unweave the lasso and retie the belt.
The Appaloosa which portrays the title character was actually a registered Appaloosa stallion named Cojo Rojo. He was born in 1960 and just prior to being used for the film he was racing on the California tracks. He sired several foals, including several race champions. During filming a few other similarly marked horses were used as stunt horses, but the majority of work was done by Cojo Rojo.
The gang would just go after Matt for revenge afterwards.
It is unexplained how Trini managed to lift Matt onto his horse.