Does look like its been over wet, clearly the carpet fitter told them about delamination they would not ordinarily know that term.
Cheap carpet poorly constructed, as this is, with a weak backing adhesive can break down pretty quickly especially with moisture, aggressive use of the wand on soiled areas and time.
Looks like you may have a a claim on your hands but of course you are perfectly at liberty to have it inspected yourself, maybe pay a visit, see if other areas are still damp or delaminating and if they are holds your hands and admit it, you can still win the situation around with good after service.
You never know you might be able to trace it back to a radiator pipe under the boards or similar, we had this with a pipe under concrete on the ground floor of a house, carpet fitter accused us of over wetting, on inspection I found he had tacked the carpet rods down under the rad and straight into a pipe, when he should have used adhesive knowing that pipes were underground.