Correct. People with focus issues do not necessarily have ADHD. That requires meeting a defined set of diagnostic criteria, including that it has an impairing effect on an individual's life.
Also, just because it seems like a simple lack of focus to you externally, that does not mean the person does not have a disorder.
Also, just because it seems like a simple lack of focus to you externally, that does not mean the person does not have a disorder.