Just a lay observation here. A wide range of "herbal" products, diet products, and various nutritional and other "supplements" are sold in the United States. By law, most are exempt from government regulation or oversight. Many products or key ingredients are imported from overseas. When laboratory analysis has been done, it occasionally reveals unexpected and even dangerous ingredients, contaminants, drugs, or potential interactions.
Some substances (whether ingredients or contaminants) can significantly affect a person's mental state, inducing symptoms such as hallucinations, paranoia, disoriented thinking, intense religious experiences, and more.
It can be especially disorienting if the person doesn't realize what is happening to him and why (as opposed to someone who knowingly ingests an hallucinogenic substance).
Until more is known, I wouldn't exclude the possibility that the Captain could have ingested some such product, and experienced a bad reaction to it. (Unless there is a categorical ban on pilots taking herbal and other supplements, of which I am unaware).
Even if it did not trigger this incident, perhaps something to keep in the back of your mind if you or a colleague ever experience such a situation.