it is the installer of the floor who is at fault what ever happens, because it is not fitted to the manufactures instructions of the laminate flooring. and i bet the laminate details does'nt say anything about not using a mop on it ?,thats a proper way to clean a floor is'nt it. hes trying it on, he must of noticed it before , and why did'nt he mention it before ?. this must be alarms ringing in your head, ditch him asap hes TROUBLE !!!!!!.
anyway all laminate flooring eventually wraps it depends how its fitted ie gap around edge, underlay, glueing if needed and general workmanship.
if i was you i would wait until he has made an official complant before telling anyone. if they do, get solicitor or insurance to investigate and im sure you would be cleared of any blame, i personally think they wont go that far they are just trying it on, especially if they have to put there money where their mouth is.
anyway thinking about it it must of been warping for ages it does'nt happen overnight. i know what im talking about i used to be a carpenter and i've fitted loads. just try to see who actually installed it,try not to sound like your enquiring about the floor,just cover your ass. if it was the home owner (probably was ) your safe, because he is not deemed professional in the eye of the law.
what ever you do dont submit, because im pretty sure they dont have a chance.
it may pay to get a free hour with solicitor to see where you stand, only if they take it further. just hang in there.
i hate people like that, out to get what they can. especially when your doing them a good service.
good luck paul