I was pretty confident that it was taken out intentionally.
It was amazing that the bilge kept up with it. Now, I happened to bilge it out of habit when I was lowering it in the water, and did note that it had more water than I would have expected after a little bit of rain overnight. Once on plane with the bilge on there was very little water on board, but as soon as we stopped it was clear water was coming pouring in!

When I was a kid we had an outboard boat, and back then there were no "splash wells" or anything like that. We'd ski and start and stop, taking in water over the transom. We put the flip-type rubber drain plug on the inside, and periodically would move the 6-gallon gas tank and pull the plug running wide open to drain all the water out. Simpler times!

A drain plug, even if it is only snug, doesn't just fall out.

LOL.....I too can remember doing the same thing.

Padraig