Well, it kinda is if you take the Saudi Arabian fella's dialogue. Then Hizaji Arabic (which essentially is GCC Arabic to put it in PDF terms lol) and is basically the predominant, Saudi Arabian Arabic spoken through the entire western portion of SA and the eastern portion as well where you can include all the Emirati Arabic and even large portions of Yemeni Arabic. The only slight variations would be Omani and Bahrain Arabic but for me, when I listen to all of that (and being from Egypt), it's pretty inclusive as it's all very connected to Hizaji Arabic.
So just because that fella doesn't say "Hejazi" specifically doesn't mean it's not spoken there when it's predominantly the main Arabic for Saudi Arabia and all the ones I mentioned.
But what's funny about much of what you hear in these videos, is the outside influence of wherever some of those people are living. You can easily pick up on some of that kind of thing if you listen enough and have lived it through your life. For example, you can clearly hear the French in the Moroccan Arabic which is VERY STRANGE for this kid and million other Arabs will tell you the same thing. The Lebanese fella's Arabic might be close to Shamy or Lubnany, but you can tell wherever he is, his Arabic is influenced by whatever predominant language he speaks since I've been to Lebanon several times in my 54 years and both my brothers were in boarding school there, the pure Lebanese is much more fluent and with a lot more "Shamy" influence than what that fella was speaking. Same with the Saudi fella. You can tell he even pronounced the Franco/Arabic in the Moroccan girl's speech very well. And so the Arabic they're speaking is perfectly fine for what it is. Just don't try too hard to "authenticate" any precise Arabic regional dialects from these youngsters is all I would say.
Then you have what is really something rather interesting in that Egyptian Arabic (and you can clearly hear it with that girl speaking as if she is right out of Boolak El Dakroor in southern Cairo!) but Egyptian Arabic is like none other. It is probably the most colloquial form of Arabic spoken out of all the countries and directly over the border from us, our Palestinian brothers and sisters' speak an Arabic that I would say is much closer to Shamy Arabic than our Egyptian. But once you have official statements being made on television or the news etc., even our Egyptian Arabic turns into its own form of classical Arabic that is much closer to a combination of the others.
That's really why you'll see those kids either get it 100% right away, or not understand it whatsoever just like what was happening in that video.