Yeah, as far as I can see it's just the one spring. They actually sidestep that somewhat, we'll see if the pictures can show it. There's a plastic hook coming from the top/north side of the switch, and it is into that hook and that is where the spring actually sits. There is a cutout on the same side of the key, which either allows the plastic of the key to move past the hook and bottom out or the hook catches the end of the cutout and is the bottom out. I'm not sure if it's just the spring which eventually gets pushed down enough to touch the membrane or if it's just they plastic of the key itself which does, either way there's a good amount of travel left after actuation.
Also in case anyone was wondering the springs in the keys just stay in place, I didn't put them back in every time. I haven't even tried to remove them.
But yeah, it's actually a pretty good feeling switch, although I don't have much experience with linears. I take it whatever this is its pretty rare.