It's plausible that anything could have happen. We just don't know what really happen because we weren't there to witness it. We can all assume in the different ideas be bring to the table. In shamanism, we believe zaj took him. In Christianity, we believe god took him.
We may believe what we want, but we KNOW he didn't know how to swim, didn't have a life jacket, fell overboard, and drowned. That's all there is to it. No need to bring in leprechauns, dragons, black magic, etc. These things are way beyond human understanding anyway.
Muskies have attacked swimmers.
Attacked, yes. But attack, drown, and kill? There has never been a case of human death by muskie. Muskie, alligator gar, flathead catfish, snapping turtles (common snapper are more aggressive than alligator snappers), otters (very territorial), these creatures will sometimes attack a human unprovoked. More often than not, it is a territorial aggression reaction or it thinks a pinky, a toe, or a shiny ring on a finger is prey. But never would any of these creature actively pursue a human for the purpose of consuming as food. The only North American animals that will attack a human with the intent to kill and consume us for food are polar bear, brown bear, timber wolf, a few shark species (most notably tiger shark), and coyotes will try to attack and take away children but rarely will attack an adult human for food.