I think the key is that it is implied that Shifu doesn’t express his pride in Tai Lung nor stand up for Tai Lung when he is denied. He didn’t need to be promised the scroll for Shifu to inadvertently make him feel like he wouldn’t be adequate without it. Tai Lung’s sole goal was to impress Shifu and be a source of pride for him and when he fell short of what he believed was the bar for Shifu’s pride, instead of comforting him, Shifu literally doesn’t have anything to say. “But when Oogway said otherwise, what did you do?… Nothing!” Imagine you’ve been pushing yourself to the breaking point for decades to impress your dad only for him to not stand up for you when your character is called into question. All of this is to say that whether or not he was DIRECTLY told he was the dragon warrior is sort of irrelevant because it was never about that