Sure it does.
"You agree that by submitting content to our service, you are granting a non-revokable, perpetual license to said content."
In which case you don't own it.
I'm not sure that follows. It's quite possible to own some land, but for someone else to have (say) a right of way over it - either that you've granted yourself, or that has arisen some other way. Such a right of way doesn't stop you using the land agriculturally, building on it, selling it, granting rights over it to other people, or forbidding third parties to use the land. You don't, however, have the power to revoke the right of way.
In such a situation, you are still the owner of the land, legally and in an everyday sense. Some people would argue that the situation with data is the same - you may remain the owner, but someone else can still have rights over it.