he's saying without reading the details of the study, people who accept the alternative hypothesis would parade around falsely-claiming "we told you so" (DMT is produced in the brain).
I've read articles on the matter for 21 years, studied biochemistry, and more importantly, metabolism. To date, there has been no evidence for INMT expression in the human brain cortex, much less the pineal gland; however, it was found that DMT may be stored in neural vesicles. Since it readily diffuses across the BBB, it's more plausible that production occurs in the peripheral tissues, where INMT is expressed, and camps out in said vesicles. For what purpose, who knows.
Using logic and common sense, it wouldn't seem likely DMT production occurs in the brain, since >90% of serotonin production occurs in the gut. DMT production occurs as a side-reaction, which is not genetically preferred, after AADC (aromatic- aminoacid decarboxlase) removes the CO2, a rate-determining step. DMT production inhibits serotonin production, and vice versa, via feedback inhibition. It would seem more likely that production would occur in the gut, and surrounding tissues/epithelial cells, where INMT is known to be expressed.