TJRE
The rationale may include the intent to educate, entertain, sell a product, or promote a certain point of view. Some sources may even (intentionally or not) provide inaccurate or false information.
Entertain
Authority is important in judging the credibility of the author's assertions. The author should have knowledge and experience with the topic. Look for an "About the Author" section of a book or website or do a Google search for the author's name to learn more.
Guest expertise unknown, Joe Rogan is not an expert or authority in epidemiology
Date is important to note because information changes over time. Depending on where on the information time line it is created details could be inaccurate or even obsolete.
May 2020
Too Soon
Information presented as fact should be supported by cited sources. For example, if there is a claim that says "studies show" a particular fact, that study should be cited so you can review and verify that it exists and is credible.
Unknown expertise of guest and Joe Rogan is an entertainer
Relevance is important because you are expected to support your ideas with related, pertinent information. For example, a source detailing Einstein's marriage would not be very relevant to a paper about his scientific theories.
Topic of "Herd Immunity" is relevant, however, this podcast serves as a research starter, further research is needed.