I'm not sure what you're referring to either.
It would help if you could give an exact time that the thing you mean occurs.
I don't hear Eric doing it there, but for sure on flute and many Low Whistles you can do a thing I've heard called "playing between the octaves".
If a flute's cork is positioned at exactly the right spot you can play a note (G for example) in the low octave, creating a pure low-octave note, then you can introduce a tiny bit of the 2nd octave into the tone, then steadily increase the 2nd octave presence until the tone is 50/50 low octave/2nd octave, then keep increasing the 2nd octave component until there's no low octave left and you're playing a pure 2nd octave note.
In other words there's no break between the octaves, but a continuum of relative presence.
If a Low Whistle is made just right you can do the same thing.
Some of the old-school honky fluteplayers would sit right on that middle ground and play with the gritty energized tone that results.
Here was the best demo of doing this on flute that I could find quickly on YouTube. Yes it's jazz but no matter what style you're playing on flute the physics of the flute work the same
https://www.youtube.com/watch?v=7owW7M02f14Another technique on flute and Low Whistles is using the break as an expressive device.
To me the effect is best heard not with Irish flutes and whistles but with the Caval, a huge bass whistle from Romania. At the beginning here he's staying in the upper octave but he lets low notes peak through now and then, a really cool effect. Then when he goes down into the low octave it's an amazing change in tone
https://www.youtube.com/watch?v=VhjGgPbQTkMHere it's demonstrated how these big whistles work
https://www.youtube.com/watch?v=pfneqMZNNPAYou can do these things on Low Whistle but they're not quite as dramatic as on Caval. I think the lower the whistle the better; these things work best on my Bass A whistle.