It's most noticable on the first rep, then you get better, but I don't think it's a big point. I assume sumo deads are like regular deads, where the descent should pretty much mirror the ascent. So on the way up, you keep your back at the same angle whilst extending the legs, then when the bar clears the knees, you push with the hips, straighten the back and lock out. On the way down, you do the reverse - lower using your back first, then the knees.
On the first rep, it looks like you begin the descent by bending the knees, and because you haven't leant forward with your back, it looks like you're having to flare the knees out to get the bar past them. Watch the red colouring on your bottoms.
I wish someone else would reply. Maybe I'm making a fuss over nothing.