2005 Hyundai Santa Fe Seized, but why?

I was driving in town (25 mph) Came to a stop, When I left the stop the car drove about 10 ft. And died. When I tried to restart the car you could only hear the starter trying to engage. The next day I had the starter bench and load tested, it tested good. My next step was to pull the plugs and try turning the crank with a breaker bar, the engine is seized tight. I pulled the top half of the timing cover and the belt is fine. I had just changed the oil 2 weeks before this happened. When the car died there was no Knocks bangs or screeches. The oil still shows full and it is bright with no burnt smell. I put penetrant oil in the cylinders 24 hrs. Ago and tried the breaker bar again and is still froze TIGHT. This is usually a no oil problem, but this was not the case. Do you have any ideas? I would hate to sell the car "CHEAP" and find out it was something simple.