Ideas why he was stuck down there and wasn't when he reached the surface:
the carabiner reaches the tennisball with the lanyard already slightly "wrapped" around the diveline - carabiner stops and the wrapped lanyard falls further down under the tennisball thereby building a kind of "loop" which is thightening as soon as the diver starts to ascend again.
This loop will mostlikely get loose as soon as there is no more weight on it keeping it closed. So when he stopped swimming the entanglement was most likely gone, too late though.
Thats maybe why the tennisball was moved and the lanyard wasn't still stuck at the surface.
the carabiner reaches the tennisball with the lanyard already slightly "wrapped" around the diveline - carabiner stops and the wrapped lanyard falls further down under the tennisball thereby building a kind of "loop" which is thightening as soon as the diver starts to ascend again.
This loop will mostlikely get loose as soon as there is no more weight on it keeping it closed. So when he stopped swimming the entanglement was most likely gone, too late though.
Thats maybe why the tennisball was moved and the lanyard wasn't still stuck at the surface.