Could you explain what you mean by fluid? Becuase to me, after reading what you posted is sounds like the US version is robotic and we more like boards..

The concept of retsev, was initiated and introduced into the IKMA curriculum by current IKMA grandmaster Haim Gidon.

It's the idea of constant movement, from one technique flowing thru to another and another and another, until your opponent is finished. Perhaps that's what he's referring to.

Like I said about the canadian fellow I met yesterday, he will be testing for leel 3 soon and was a bit behind and had no concept of retsev and the whole continuous movement thing.

I think that's what he may have meant. Correct me if I'm wrong.
Be safe, If not kick someones ass.