For me, the difference is not clear. Any way predatory journals have no true editorial board, no peer review system and are often found to publish mediocre or even worthless papers and asking huge charges.
For finding out, if a given journal is predatory or not. These sites discussed that
"Beall's List", a report that was regularly updated by Jeffrey Beall of the University of Colorado until January 2017, set forth criteria for categorizing publications as predatory ( https://beallslist.weebly.com/ )
I don't think that they are the same. because motivations and pruposes aren't the same.
most of the standalone journals are the result of an individual efforts of academics and scientifics from universities and labs, to make the publishing act more democratic, not only for the big multi-nationals publisher companies who rule the world of scientific publishing with profits which make it a pure industry. the standalone journals are publishing only single title journal and usually it is open-access without any fees to publish, only with online release (there is no more paper publications any more for the most of journals).
the predatory journals try to reach the same statue (being themselves a big publishing companies) by dense and intensive mailing (usually as spams) to any one in the scientific and academic circles, potentially able to write and submit a research paper. They learn about to get a label (Thomson, Scopus, ...) and they apply it by increasing their publications and citations to be elligible to the IF affiliation, of course in the aim to sell more subscribing from academic and university institutions.