One must assume that it has been the issue at some time in the past.
You might have felt bad with the answer he gave you, but I feel bad for him... Often that answer he gave, is actually helpful to people contacting him.
Yes but troubleshooting 101 says before replying copy and paste what the customer sent you into a browser, remove the period, try navigating to that URI. If I can access it without problem then the potential of it being a typo on the customer's part is probable. Whereas if removing the period produces the same result as indicated in the ticket then I would begin looking into it in other ways before just assuming the customer is clueless and responding to them as such.