It may come down to "showing your work". The post talks about how they investigated the two suspect submissions by asking them for evidence of their process, but none was forthcoming.

It may just start to become the norm for publishers to do this for all submissions, like checking references for a prospective employee.

I have very little physical evidence of any book I've ever worked on, but I'm sure I could find heaps of digital versions and notes. I hope this would be good enough although obviously it could be falsified by someone determined enough I guess (note to self, start writing notes by hand)