i was watching the first video calum Von M. made when he went back to the gym after the bicep injury explaining the reason on why he might have injured him self, can you help me confirm if that is true

https://www.youtube.com/watch?v=P3byNJ8MeuM i was watching this and for the first time i got real scared bcs i always thought that the straight arm was the full range of motion , but then realized the bicep is already stretched 100% before you complete that full range of motion of the arm, so he says tendons are the ones doing the rest of that motion not the bicep. but then i watch other youtubers or body builders with a whole other philosophy on that . example Kai green "i will never be a weightlifter" https://www.youtube.com/watch?v=m8wZNGL4iA4 where he explains full range of motion and using reasonable weights, but they way he shows the exercise is a complete opposite compared to Claumns suggestion, can someone please help me clear this up . (1:53 - for kai greene example )