Brendan Allen isn't mincing his words after pulling off a short-notice upset win against Reinier de Ridder ... telling TMZ Sports his opponent's team wasn't responsible for calling it quits, but the fighter himself!!

We chopped it up with Allen following his massive performance at UFC Vancouver over the weekend ... which ended when RDR failed to answer the bell to start the fifth round. Getty

Allen said he watched back the moment RDR's corner threw in the towel ... and while Reinier's coaches swore it was their call, he had a different view.

"It was something to the fact, 'Are you okay, are you okay to keep going,' or something like that," he said. "And he said, 'No.' They said, 'Are you done?' He said, 'Yes.'"

"It had nothing to do with his coaches. It had nothing to do with h

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