Thanks for the link. It is a very interesting read.
In particular it also says this:
To avoid both signals being added by the system, a priority P/B is provided on each stick. By pressing this button, a pilot may cancel the inputs of the other pilot.
Yes, indeed, I have not found any reliable source for the claim that both pilots were making significant stick inputs simultaneously for any extended period of time.
"When both sticks are moved simultaneously, the system adds the signals of both pilots algebraically."