The wording has a cool history. It's a real rhetorical device.
It comes from the man on the Clapham omnibus, a common law legal reference first used in a case McQuire v. Western Morning News in England in 1903. "A reasonable man" is a hypothetical individual. It is not a real person, but rather a rhetorical device used to ask an audience, in the former case a jury, what would constitute as reasonable or unreasonable in a given context.
Since then, it expanded to other legal concepts beyond negligence, and expanded to other non-legal contexts such as intellectual and philosophical debate. For example, you will see it used in noise ordinances, where the text will say something like "a reasonable person of ordinary sensitivity." Or in the middle of a philosophical debate, an opponent would suggest that a certain premise be taken on the basis of what is reasonable. Or in web design guidelines, where a designer is asked to give a reasonable attempt at design that would aid those with disabilities.
What they all have in common is that it's a normative concept designed to give us room to interpret the facts on a case by case basis. We have no empirical measurement. We're supposed to agree and disagree about it, but the goal is to understand that it's based on what is ordinary and normal.
It's certainly philosophical in nature, but it's quite useful. It should not be considered a qualifier about a person, but rather the act and the interpretation of that act.
A Reasonable Person would agree.