why would my plug pop out if i had anti freeze in it?

 

My other brand 3/4 ton had antifreeze in it a couple years ago, good for only around 20 degrees. I knew it was marginal, but since it usually doesn't get too cold around here put off adding more. One night it dropped to something like 12 or 15. When I checked the radiator that morning there was slush at the top.