Yes, one of those tickets sold for 5/13 is me.

It doesn't seem to correspond to how full the train is, as you have seen. My guess would be either, a. why not price it high and see who bites? There's plenty of time to lower it if demand doesn't materialize now that trains generally sell out by the hour of departure or b. some history is showing specific trains on specific dates are reliable sellouts and therefore should be priced higher (I've noticed April trains have been slower to come down in price, eg.).