He meant there's a chance you're confusing a freewheel with a fixed cog.
Foot retention is pretty much a requirement to skid. Unless you're doing sw8 leg overs.
Ok let's see If I'm correct; a freewheel is when the wheel keeps rotating even when you don't pedal right? And a fixed cog is when the pedals don't stop turning and you have to keep pedaling... Right?
And by foot retention you mean pedal foot straps?