They are spells, just not spells of 1st level or higher. Most everything that is meant to keep cantrips in check uses that language, you can't use spell slots on them, you can't add them to spell books, stuff like that, because they might be spells but they are not 1st level or higher.
Under the Spellcasting section of the PHB it talks about cantrips being 0 level spells.