They have to be much less than 1%, I don’t t see how the math works. Views (and ad clicks) are what matter, not posts and comments. They only need the posts and comments to have something to stick an ad next to.
I say this in jest, but only partially... lots of subreddits have noticed influexes of AI bots recently. Maybe spammers testing the water, or maybe you were just the product that was just helping train its replacement.