I haven't yet had an experience of this, but this presumably was a A321 NEO flight. BA actually can't sell all the seats on it at the moment due to the risk that you mentioned, more details in the main NEO thread. There's some software modification needed before EASA will approve full loads. I am surprised that the captain's words were respected, when I read in that thread of this possibility I felt that someone, somewhere, would think this doesn't apply to them and before you know it everyone would be up on their feet.

I have been on flights where they couldn't open doors due to the risk of a strong gust of wind would roll the aircraft over.