That starting technique is a tumbling mistake and one that I’m certain cost those athletes hundredths, or more.
The extended trail leg almost completely obviates the power it is capable of generating in a more conventional stance in which it is bent. It’s essentially a one legged start.
I was absolutely shocked to see this being used; particularly by the players with T&F backgrounds. My initial thought was that the T&F athletes would have immediately questioned the competence of whoever instructed them to use that stance.
Done that way the forward leg then becomes solely responsible for driving out of the start position.