Pretty sure YT will play back in whatever is ok for the device / drivers used.
Eg. often my vids playback in 480 or 720 when viewed on the phone, on my desktop, it will play the usual 1080 I record in.
The original Iceland video plays auto in 1080.
And looks fine
The option to play up to 2160 is there too, but I guess what it's saying to me is it isn't worth it on my desktop monitor.