You'd be surprised at how many people upload pictures showing their id to public sites. And even if it's not that, then it might be an inside job by a family member, friend, co-worker, etc who had once enough access to the id to snap a pic of it.
Also, chances are that if you can convincingly create deepfakes in general you can (deep)fake a picture of an id to a degree it will be accepted by OnlyFans and other services, especially if these ids are from places the staff might not be entirely familiar with. Do you know for example what a Columbian or Polish or Turkish or Cambodian id should look like and what security features that you could see on a mere picture of it should be present, if there are even such features?
I've seen such id fakes done in practice, though that wasn't related to OnlyFans.
That's why when I was in a position where I sometimes had to verify identities, I would not accept pictures of ids, I would ask for a "proof-of-life"/"timestamp" style pictures you see commonly used on pseudonymous sites like reddit or 4chan to establish authenticity of a poster. Those are not impossible to fake, but a lot harder, especially if you limit the time in which the other party can respond.
I don't know if OnlyFans adopted such a method of verification by now, but I know they used to accept just ids.
I also online-know a guy who says he used to run an OnlyFans scam where he would seek out underrated accounts, steal their content and republish it under his own accounts. That obviously required he create a lot of verified accounts with valid ways to pay out, of course. He never went into details on that. He could be lying about the thing, but when it came to other things he claimed over the years, a lot of it was verifiable true, so I don't know.
You can also buy verified OnlyFans accounts on the black market (hacked usually) or compromise accounts yourself. A lot of OnlyFans accounts are completely inactive, abandoned by the original owners, so they will probably not even notice if it gets taken. From there you can replace all the account content as you please, and I believe in the case of OnlyFans even change the user name and probably update the payout method and information as well.
As for banking information... that's harder, but there are probably some ways left. The question is if the OnlyFans account in this case was even made for financial gain, or just to cause humiliation, in which case subscriptions might have been free or the money might have never been collected by whoever created the account.