Your explanation gave me the aha moment I needed to start picking up this concept. Thank you for that!

One of the biggest ways to figure out if a sentence is "Context" is to see if the sentence is in the author's POV or "voice". The first sentence is not context because it is the definition of Premise that they gave in the summary a couple slides back that is a "statement providing support for another statement" which this sentence is. If the first statement were something like "Some scientists claim that....." then it would change the structure of the entire passage. Let me know if that makes sense.