Understood.
While some psychedelics have included flying saucers among their visions I am not familiar with any case where the gray aliens were part of those particular visions.
There have been so many gray alien sightings around the world that we have a detailed knowledge of their characteristics—the large black eyes that seem to communicate visions to humans, the small height, the tiny long fingers, the skin that seems almost artificial or clothes-like, etc etc etc.
I am convinced they are not drug induced hallucinations of any kind.
Terence McKenna has described in great detail aliens seen during drug trips—DMT generates one type of alien, psilocybin another, for example.
IIRC Jacques Vallee did a documentary video on a contact story in Argentina with a young gaucho named Juan Perez that involved Indians (related to Perez) who had the same kind of experiences. I can't remember if the ayahuasca/gray alien nexus was in the documentary or in some related follow-on research that I had done.