Ephedra is a beta-2 agonist which also temporairly boosts circulating levels of dopamine in the brain. Alcohol also has some mild dopamine agonist activity. Most of marijuana's intoxicating effects are though to be mediated through what is known as the anandamine receptor (this is what thc bonds to), but some research also suggest dopamine agoinist activity as well. Pot is also a known beta-2 agonist - it increases blood pressure heart-rate etc.
To sum it up your friend had a dopaminergic episode similiar to what is refered to as "ampheatamine psycosis". Vivid hallucinations and schizophrenic like dellusions are hallmarks of this temporairy condition. Goes to show you why mixing rec drugs is profoundly stupid. Did he require a vist to a local ER?