Even Ian Anderson mocks that decision by the Grammys, and it was their decision that got him the aware, lol.
What makes it even funnier, in the early 70's, Tull WAS heavy compared to most music out there...I mean, only Sabbath and Zep were really doing heavier music in 1970. So yeah, at that point, a case at least COULD be argued for them being "metal"(and they WERE hugely influential on a lot of metal that came afterwards, a lot of people don't realize just how much so). But by the time Crest of a Knave rolled around(that was the album that won the Grammy), there was no way you could even argue them being metal(and they certainly didn't consider themselves metal). Ian is pretty sure they only won it as a sort of "late acknowledgement" of their influence on the genre, rather than because they actually deserved to win it for that album.