I was watching a rear view of the Seoul final. Ben’s foot is planted almost perpendicular to the lane and his thigh looks to be laterally rotated. 
Is this taught or was it specific/natural to BJ?
Is this supposed to be good or bad? I think that when a sprinter gets very strong his first foot plants need to be sideways … if they are pointing to the front I would think you can’t stay low for long or get enough traction in those first steps.
seems like most elite sprinters do this. Early in the race you can waste a little motion in order to develop more power through your hips.
I think there are two reasons for this. The first is that when you leave with such a low departure angle, there is not time to get the foot all the way up to the front before you hit the ground again. In addition, since it is the start, there is not even the elastic recoil off the ground to help the hip flexor.
Secondly, I think the hips may be able to generate more power with the thigh somewhat laterally rotated. Imagine a heavy squat…most lifters have their toes somewhat turned out.
That said, I don’t think one should consciously attempt to do this - it just happens naturally.
Agree with xlr8. This was a natural action- not taught, or in need of correction by Paul Chek!