That is purely conjecture, you cannot know this, not with anonymous accounts.
Most authors' accounts are pseudonymous, not anonymous. They have clear and distinct identities, just not under their official names.
Diversifying your posting activities over many accounts is financially punishing. You will lose out on auto-votes, your alts don't typically have as many followers as you do, nor do they have a standing in the community like you have if you've been posting for years.
There is no reason to assume this.
I think it's a very reasonable assumption because there are thousands of accounts posting very diverse content on a daily basis and earning author rewards. All of those accounts earn curation rewards as well. Do you really believe the small number of whales or orcas on Hive have time to post thousands of posts on a daily basis?