I'm way inland and my water table is not connected to the ocean swells. It is aligned with a nearby creek water level that does not rise and fall from what I've seen over many game days. I'm still leaning toward Loki pulling a prank and had a pig roasting party with my boars.

I could see an ocean swell lifting boars up and out of their pen if the heights were right. I have a seaside base that I built up to prevent that.