While we did our best to make sure the setup is level and the apparatus is precise, the video shows the balls actually land about 0.02 s apart from each other (the slow-motion part was done in 60 fps, and there seems to be a difference of about 1 frame). We consider this difference to be negligibly small. Normally the apparatus is positioned about 2 meters above the floor, and the difference in landing time is just as imperceptible.
You will notice the "drop-ball" bounces towards the center of the picture. We think this is mostly because the concrete floor has small pockmarks and other local irregularities, which on average combine to form a level surface but individually can cause funny bounces. The ball may also have a very small horizontal velocity due to the way in which it is dropped.