Personally I think this is great, regardless of how easy or hard the particular song is to play, because it's great to see young players/fans playing this kind of stuff at such an early age. When I was in high school it was murder trying to find people who would (and could) cover stuff like Kreator and Voivod. They might not have the song completely "nailed" as it were, but if they're already on this path now, by the time they're older they could have developed into really outstanding musicians, not unlike people like Mike covering Pestilence or something in his earlier days! These kids could be playing Green Day and Nickelback songs and instead they're covering Opeth, that gets a huge applause from me, frankly.
Oh the memories of playing these outdoor gigs in high school, with bad amplification and not being able to hear each other.....I think I still have nightmares about it from time to time, haha. Playing technical music and doing it cleanly and tightly under those conditions is a feat for anyone actually.