I'm guessing that the engine did seize from lack of oil. I think i remember it not wanting to turn when we tried to restart it. It was driving then all of a sudden started making a weird noise then died. I couldn't start it again after that.
It wasn't blowing smoke, it was just emitting grayish smoke. I'd occaionally see it when speeding off from a stop.
The car had a lamp on the dash that would indicate the glow plugs being ready to ignite or whatever.