If you're dealing in probabilities, that's not threat modeling; it might be in the larger umbrella of risk management though. Defining a threat model means to qualify what sort of attacker you expect to face and what they are assumed to be capable of. An assumption such as "this adversary can send arbitrary packets to the public IP address" is what would be documented in a threat model.

The raison d'etre of threat modeling is to methodically tackle the actual or assumed risks that an attacker can pose against you. It is not an exercise in swinging at shadows, though I wouldn't discourage overstating the capabilities of an attacker, if needing to protect assets like patient info or PII. Doing threat modeling based on "gut feeling" is a recipe for not recognizing risk where it's present and seeing risk when there isn't any.

The fact remains: you cannot squeeze blood from a stone. Even the most sophisticated AI cannot steal PII from a computer that doesn't store PII. Proper threat modeling means you don't put anything on the line that you haven't squared up against the risks, however improbable. For any non-zero concern, a good threat model will discuss its mitigation, whether it will be absorbed, or if it is an open question. For an out-of-scope concern, a good threat model will explicitly state that assumption.