when people respond to a post or comment like, "everyone does this, it's not just [adhd/inattentive/disorder], it's called being a person."

Yeah and everyone coughs once in a while but it doesn't mean someone with pneumonia doesn't cough?? It doesn't mean pneumonia doesn't cause coughing??

Everyone gets dizzy once in a while but it doesn't mean vertigo doesn't exist??

Just about every symptom or group-common trait is going to be experienced by people who don't belong to those groups or have that disorder. It's about the frequency and intensity with which that symptom or trait comes up.