I have. Regardless of the hedging he does afterwards, it's simply plain and unambiguously wrong that pot is linked to mental illness.
Unfortunately, it is not near so unambiguous. There is growing research that does make a link between marijuana use and schizophrenia. Just to be clear, "link" does not necessarily mean causation, but people with schizophrenia use marijuana at a much higher rate than the general populace. Of course, they could be self-medicating. Newer research, however, does suggest that use during adolescence may trigger early onset of the disease. Who knows, really; more research definitely needs to be done. All I'll say is this, if there were a family history of the disease, I would strongly discourage my teenage children from using marijuana.