As you can see in the video, when entering the 3 block tall area under the tree you walk slower than usual. Not sure if this is intended, but just in case, here is the bug report.
MC-257342
You get slowed down when riding a camel in a 3 block tall area
Resolved
Fixed
4
In third person view, you can see that the player automatically sneaks under the block. That auto sneak is what causes you to slow down.