Hurling propane tank loading technique - GIF

[Frank S]

What am I missing here? The buckets do not hit the truck, nor do they appear to have a tether, but they change direction in midair.

A carefully practiced lift toss and release movement of his hands.1 hand is still in the motion of lift while the other briefly halts just as he releases the bucket. The action causes the bucket to begin its rotation while kinetic energy still propels it upward