Yes, you are responsible. You would have to give the chairs back or give the value. You should claim your public liability insurance if you think this could be a high value claim. Happy to discuss.
Given that there was no acknowledgement for what looks like over five years from you to him, it is likely that his claim is time barred. Can you check that you didn't acknowledge his claim for a period of over five years. If so I think the law of prescription applies and his claim would not stand up in court.