Uuh no that is caused by the overflow. Though the build does stack a bunch of speed by using the teapot and medusas ultimate that makes all attacks heal. I'll check the typical speed it gets to (outside of winter mission)
Edit: yeah Normal speed stacking with the build is closer to like 9 - 11 it uses the teapot on the airplane lady in combination with medusas ult to stack speed with every hit. It is possible to use the paladin armour that grants heal on hit to make it staci further but you lose out on damage then iirc.