Depends on the species of penguin. There are some big ones as well as little guys! Also that penguin might be on the younger side, given that it seems pretty curious about the world.

I'm not a marine biologist though, so treat this with a grain of salt

Emperor penguins are big, like 4' iirc, but are the largest species. Most penguins are more like the size of an ordinary bird like a duck or a goose or whatever

They go from being the size and weight of a liter of yoghurt (the aptly named Little penguin) to as tall as a zebra and as heavy as a Rottweiler dog (Emperor penguins)

Emperor penguins get up to 3' but those are the largest species, the others range in sizes but most aren't that big

Probably just a random instinct that was reinforced by survival of the fittest (at group population levels) because it meant that group didn't contaminate their nests or water with the dead, which would also attract scavengers that might also try to prey on living penguins when there weren't any already dead handy.

Or maybe they go to get frozen so that when a future penguin solves the problem of death, they can go and unfreeze the frozen penguins and use that massive undead penguin army to conquer more southern islands.

Because they know it's coming, and now's the best time to find out what's out there.

Unless proven otherwise I choose to believe that it was the same as with the penguin in the Werner Herzog documentary and the bird quickly returned to their flock moments later. (Herzog didn't show that though because a penguin heading towards death is more dramatic)

But there's no such thing as land predators.

What, humans? No, we are omnivores, occasional predators.