You brought up a good example, if one did not understand or read cantonese one would ask these questions and perhaps misinterprete the story.
No, Master Gwok Fu said he was being taught by Master Yip Man, and Master Yuen was sitting right next to him. Apparently, this scene of Yip Man teaching, and Master Yuen being there was a common thing.
Next he said Master Yuen was ruthless and quick in his strikes when they played hands. I dont believe Master Yuen was out to do him in, maybe just test him. And he said, he was able to handle the exchange. It doesnt mean, he beat up Master Yuen. Or Master Yuen beat him down. He didnt say that. He also went on to say Master Yuen later told his peers that Gwok Fu was a skilled fighter.
We can exchange skills without doing the guy in right? In chinese martial arts, there is a saying, once you touch hands, the true kungfu will be reveal.
Yiu Choi, Yuen Kay San, Yip Man were known as the 3 Heros(of wingchun) and famous in Guangdong. I personally believe they were great friends. And in those days where Wingchun was not a publicly taught system, and expensive to learn, 3 friends who had the honour to learn it, would exchange(Me thinks it was like a Turf Club, where the Elite hang out with their race horses)
All this comes from the video featured. I am not going to add any legend or stories to it. Like I said, I wasnt there, he lived it. And I respect all three of them.
History is funny, according to what you wrote, Yiu Choi learnt from Yuen Chai Wan, and then taught Yip man. However in the chinese post from Mainland china, Yuen Kay San learnt from Ng Chun So's chum kil and bil jee after Yip Man. So who is who, what is what? Hahahaha.....no one knows and honestly none of it matters, in the big scheme of things, except to those that insist their version of the story is right. Really if Ip man was beaten up, so what? And if he lost one exchange(who knows his mental state), maybe he had a off day, does that mean he is not a great master, or will not be? See there's where stories dont continue or dont teach.
In chinese we know as a warrior, winning and losing is common. What is important is what you do about it, after you have had a fall- to pick yourself up and better your skills. Thats really winning.
When I was training in army, they taught us, we can lose the battle, we cannot lose the war.