As the rod spins up with an attached mass whose center of gravity is offset from the end of the rod the outward-directed centrifugal force on that offset mass produces a moment on the end of the rod. That causes the rod to bend in a direction that is opposite to the offset of the c.g. of the attached mass.
The apparent bendform observed when the rod is vertical is considerably different than the horizontal bendform shape. That is an artifice of the scanning delays going from the top to the bottom of the frame. That end to end delay is negligible when scanning rows near the middle of the image and thus the horizontal bendform shows the true bendform shape of the rod.