I would have thought it would generate enormous wave, but that's clearly not the case. I think some of the biggest waves was generated by a mountain sliding or collapsing in the sea. I expected something similar here. Anyone know why not?

It is not a very energetic event for its size. The iceberg is floating, it can't accumulate a lot of potential energy before flipping, so when it happens, there is not enough to make big waves. The center of gravity of the iceberg barely moves.

A mountain sliding into the sea is different, these higher up rocks have a lot of potential energy, that convert into kinetic energy as they fall, which is transferred to the water as they splash down, making big waves.

The amount of water actually being displaced isn't changing much, it's just kind of rearranging around where is water and where is ice.

i suppose its not actually displacing a lot of water volume, unlike a landslide.

All its mass is already on the water so it's not displacing anything. It probably made some splashes but it seems like a fairly round object rotating rather than smashing into anything

Maybe because ice floats, and it's almost the same density as water?