It is not your customers' responsibility to ask probing questions about your stock control. If you do not communicate explicitly and openly when things are available, people will not care to know.
By your own statement, the poster's statement was completely accurate; it was out of stock and they had no idea when they would be back in stock again. Saying that they had a responsibility to chase you up because you're unable to put the information they needed on your website doesn't seem entirely fair.
These posts show you and Inertial in neither an amiable nor an edifying light, and I think you need to walk away from the computer and de-stress.
All he would have had to do to get an answer on when we'd be back in stock is ask. It doesn't seem that ever happened, which is unfortunate. Choosing to spread inaccurate information online as a result of a conclusion reached in a vacuum is a problem that extends well beyond 68kMLA, and it's societally corrosive.