Definitely the motion of the bike can carry your foot through the dead spot but it sounds to me like this fella has some bad form. Rather than spinning circles, it sounds like he's pushing down and waiting for the bike to pull his foot back to the top of the stroke.

This can be bad on a fixed gear bike just like a freewheel because it tends to jar the knee at the bottom of the stroke and uses the smaller muscle groups on the front of the leg.