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.

Here's an excellent example of the latter, from a short ways up the BC coast from me. Not caught on film, but found later by heli pilots, and on seismic data: https://hakai.org/stories/the-big-slide