Fireball requires a saving throw, so it stands to reason that it would be considered an attack spell (something not really defined in 1e). Sleep requires no attack roll or saving throw. And as I've said, it can be an offensive spell, but it's also a utility spell and isn't always an offensive spell. Light and enlarge are also listed as offensive spells in the DMG*. Are you arguing those are combat spells that would always break invisibility?
* you're leaving out the context of that list. that list isn't describing all offensive, defensive, or other spells, nor does it try to categorize the spells into those buckets as some hard and fast rule. That list is solely for the purpose of choosing which spells a MU starts out with, because in 1e, they begin with one offensive, one defensive, read magic, and one other. So that table just tells you which spells you can choose, based on that rule. Looking at that list, and it's easy to see that many of the spells fit in multiple categories if you were really truly wanting to categorize them as offensive, etc.