Jim I think the glueing was done at the edges and not all over ...I dont think any fitter would glue all over with underlay and gripper underneath as there would be no point ,but you are right the backing would come of if that was the case ,but the underlay would be pulled apart also .
I dont think the fitter who fitted the door bar is at fault as he has just said what he sees and cant for a min think he would pull all that carpet up to do a door bar or if he saw it was wet even, you would see delamination on the edge of the carpet when you do a door bar in fact it is probably the area worst affected for obvious reasons,how many times do we see carpet coming out of door bars and carpet is knackered, and I would suspect he mentioned this to said ass*hole and he put two and two together and came up with scam ( sorry did I say that ,well wash my mouth out ) ,I believe the guy did that and dare I say it had a hand in the damp problem also .
As I said before delamination does not happen instantaneously if carpet is in proper condition and given the time scale off incident I would say highly unlikely . There are many on this forum who are skilled in flood work,I dont and am no expert , but they have taken up carpet which has been submerged in water and the backing is still operational .