Yeah it’s vibrato. If it’s possible, you should flutter the finger on the hole two below the one you’re wanting to effect, so have one open hole between the hole you’re covering and the hole you’re fluttering. You should cover and uncover the hole you are fluttering.
If you do it on the hole directly below the note you’re playing I guess that would be more of a trill. If you want to vibrato the second to bottom note so E on a D whistle, you can half cover the hole below to get a similar effect.
Hope this explains well enough for you, bare in mind I’m relatively new to this too and I could be playing completely unorthodox-ly!
Think about it. If you’re fluttering on the first open vent hole below the note you’re fingering, and you make full contact (closure), what’s going to happen?
On that same note, if you flutter on a lower hole (or holes), leaving an open hole (or holes) in between, and you make full contact, what’s going to happen?
Answer those questions, and the technique follows from there. And as a practical matter, I never “hover”, but flutter to a half-hole (partial) closure instead. Much more control IMO.
I like that at 2:10 the camera[wo]man apparently can’t find the guitar soloist, who is buried in the back behind the keyboard and piano and Sharon. So the camera starts saccading around at random.