Both hybridization and displacement presupposes the existence of two species, which is the problem. It appears that the researchers made sure their conclusions fit their original assumptions.
I don’t think hybridization presupposes the existence of two species. Hybrid corn or rose strains are produced in great quantities and they are still corn or roses. I’ve read a lot of rose catalogs and spent time in Iowa and I never had the impression that either corn or roses were different species. The same cold be said about dogs.