John,a quick google did not find ANY "PSE" bow named Excalibur.
I am sure that is an honest mistake.
PSE do make crossbows,and I found at least three different models,but none called Excalibur.
It was in the the title of the ad. I checked it again and see he's changed it now to PSE. You can see the old heading though in the coding of the url. and not a word of thanks either.