Is that Phil Cunningham on the piano?
Any reason why it sounds modern and Scottish?
Getting into subtle stuff here, and it's often hard to explain. There are many things that come together to make these styles what they are. And it's not just the tunes; playing style is part of it too. You develop an ear over time if you listen to both, but it's more like a gut feeling. I like to think I can tell Scottish from Irish, and I've been known to nail it, but I've been wrong, too, especially if the tunes are from Donegal or Sliabh Luachra. But to date I've usually been able to tell a Shetland tune from a mile away.
From my American perspective I see the Irish and Scottish traditions as being closely related indeed, but once you hear the difference, these traditions are not at all identical. Spend years playing solely in the Irish idiom and then get thrown into a Scottish context, and you will learn this firsthand and in no uncertain terms. The casual Yank listener usually hears no difference between them, so I like to say that the difference between Scottish and Irish trad is that where one zigs, the other zags.
As to whether it's modern, there's that ear and gut feeling thing again. I think that Ben is likely right on both counts - Scottish and modern - on the basis of what I've been hearing out of newer compositions of that ilk. I don't know the tunes in the vid myself, so for now I'm going with that.
What is certain is that you can confidently rely on the likes of Julie Fowlis, and those she plays with, for good examples to follow.