Well, it is _possible_ that they didn’t know the journal is predatory or they had too many bad experiences with very bad reviewers.
However, one thing that stuck out to me was that they seem to emphasise that they are “led by Professor Marco Ruggiero MD, a molecular biologist and fully qualified medical doctor”. I’ve noticed that certain types of cranks have a habit of attaching the “Dr”, “Professor”, “MD” credential as a prefix (or suffix) to their name.
It seems like most people who have seriously learned anything in graduate school probably would not chose to advertise their credentials to other people, as they would probably be keenly aware of how little they know, which is vastly more than what they do know.
Furthermore, a really good piece of innovative science probably doesn’t come in the form of an 8 page paper.
So, even if given the authors were right, I don’t think they are going about it the right way to show they are right.
