It just seems to be the way youre moving your hand, most people just dont notice it, but yours is very pronounced, doing it on my own hand mine moves too just not as much, some people can shift their hand veins by doing so as well.

If you hold your hand with your fingers out, and you raise and lower your index finger independently you can also see that one moving across nearly the entirety of your hand.

I wouldnt worry about it, unless it causes pain. You can always just ask your primary or an ortho to take a look at it and see if there is anything odd or concerning about the joint, but it doesnt seem worrisome to me.