You are mistaken my english speaking french: even though the snowy owl has tiny plumicorns, their size and position make them almost invisible and commun language consider the harfangs des neiges as a chouette even though it is from the Bubo family which is the most distinctivly hibou family of them all.

Edit: After a quick wikipedia check it seems to be also classified as a member of the Strix family, which is very clearly a family of chouette .