Nothing like what you're used to in TKD, my friend. Think of kicking in a door, slamming your foot through it... then apply that as a kick to the side of the knee, where it doesn't really bend.
...You pretty much just said, as I read it, Front Stamp Kick from the Side, to the Knee. We did that last week.
Side Kick to the Front of the Knee is more common though.
Let Me be the first to say, I have never learnt to use any given Kick with the Instep to the Knee.
I was mostly curious so as to get some context behind His statement.