Thecodingdude, I always support my customers, always answer all the questions. Many hold the questions by e-mail if they do not understand something and I always help them. But I have a suspicion that this comment was not from a real customer, but from a competitor.
Even it was from a competitor (although its highly unlikely) he still paid you money (yay moneyz from the competition) and gave you a choice to present yourself as a professional or as rude and unreliable in the comment section in front of your customers. You made the wrong choice.
Just get login details and check it for yourself. If it works fine you can always record a short walkthrough video. That’ll take about 10min of your time and maybe will be helpfull for other customers.
Truth or not, that comment can do untold ongoing damage to all future releases. My advice is to post a sincere apology and learn from this. You have to pick your fights my friend.