Ingenuity disables its optical height detection system a short distance over ground because kicked up dust could interfere with it. It proceeds downwards until it makes contact with ground. To reliably detect the acceleration of that, they have to "slam it" into ground at a speed of approximately 1 m/s.

Edit: here is my old comment on this and the submitted article from which the information was taken: https://news.ycombinator.com/item?id=27009678

The author addresses that in a comment [0]

This part might not be entirely accurate due to a lack of image data around takeoff and landing. I had to make my best guess from reference video taken by the Perseverance rover on a previous flight. That landing was a little rough and showed some bounce, so I recreated that.

[0] https://twitter.com/stim3on/status/1420176001347297280

2x speed, prob not as bad in real time