yes the flutter kick here is referring to the GUE/DIR style where hips are locked and knees are bentTo add to the confusion, someone once pointed out that what GUE calls a "flutter kick" is more similar to what some cave divers (perhaps more in Mexico) call a "shuffle kick" than to the rest of the diving world's "flutter kick." GUE's flutter is a bit of an oddball.
The nice thing about GUE is that what is taught is the same everywhere in the world, so if @Imla describes a flutter kick then I believe that is the same flutter kick the OP is trying to learn.