That's actually not completely accurate.. Reddit has this bot called AutoModerator which has, among its numerous other functions, the ability to blacklist users. A blacklisted user's comments/posts will be deleted as soon as the bot sees them.

In theory, this only applies to subreddits where automoderator is installed, but in practice, automoderator is installed on every sub above a certain size simply because it does a lot of cool things.

In essence, a user can be "soft" shadowbanned this way.