Just my $0.02 worth....
Did the homeowner directly hire or pay you, or were you contracted solely to the store??
If the homeowner did NOT hire you, pay our or have any work contract with you, you are a 3rd party to the transaction. The homeowner can only take direct action against the store (that they had a contract with). The store, in turn, could then take action against you, if warranted.
However, there is another question that arises... could the homeowner make a claim that as an 'experienced' flooring installer, you should you have been aware of (and informed them of) any structural problems before installing the floor? If so, then you might have a liability issue.
My suggestion would be to contact the homeowner, in writing. Explain that you did your work in a professional manner and the work was completed in accordance with your agreement with the store. Explain that as an independent contractor FOR THE STORE, you are not directly responsible for problems that are not related to your SPECIFIC work FOR the store.
If they decide to take action against you, file a 'general denial' and state that you were not in their employ and that you had no contractual obligation to them.