Definitely not short recoil, nor long recoil. Barrel and brechblock are not locked together. I'd say blowback?
I suppose it depends on how you want to describe it. Thanks Mike for the excellent video.
As you can see in the video, the entire top of the gun works just like the standard revolver, except instead of using energy from the trigger finger pulling through a DA, to rotate the cylinder and cock the hammer, it used a camming action worked by the recoil of the gun.
Long or short recoil depends on the distance the recoiling parts travel before unlocking to eject and reload the chamber. Clearly that exact definition doesn't apply well to the Webley-Fosberry action.
Neither does the usual definition of blowback, where a bolt/slide are "blown back" from a standing (fixed) barrel. Again, the revolver design just doesn't work like that, or have exactly comparable parts.
I would call it a recoil operated revolver. A semi automatic revolver would be apt as well, I think, though not in exactly the same way a semi automatic pistol functions.
An interesting and actually functional design, but with enough practical drawbacks that it was soon passed by better designs and became an evolutionary dead end in firearms development.
but they are so freakin COOL looking, ...