Ralphm2425

Hi, i have a 350 carbed engine that has been sitting for around 15 or so years. And I wanted to do a quick test run to see if it started before i bought a new alternator and water pump for it, and after a few seconds of cranking it started up perfectly (oil was also topped off). I only let it run for 6 seconds max and did this maybe four times. But when i came back a couple hours later it seemed that the engine had seized? So i took the plugs out, poured some oil in, and now it seems to turn over fine, but i havent tried starting it again. What would cause this to happen?