Yeah, the Hobie 18SX number looks odd. Note that in Beaufort 4 it is actually rated slower than the TheMightyHobie18/18 Magnum. Maybe the 18SX is a dog, maybe nobody good sails it.

Every now and then I have to score weird boats. In my experiance they're always casual racers and get smoked by the serious sailors, so I try not to get my undies in a twist about their numbers. Your milage may vary.