One of the oldest glitches in Minecraft that still works. Actually, it is 6 years old, it still works in 1.14.
Michael discovered it, he found this in version 1.4.2. This has continued to exist in new versions...
MC-151384
Reset fall damage glitch
Resolved
Duplicate
0
Duplicate of MC-212.
By the way, when recording the video you were in Creative mode, where you can't take fall damage.