From a cognitive process standpoint, the deficits in ADHD are primarily in dysregulated attention and dysregulated inhibition. Downstream of these, you then get difficulties with organization, initiation, etc. If a person is distracted in a situation in which any reasonable person would be inattentive, then that's not particularly dysregulated. (Aka, purpose for which the word "boring" was invented.)
And moomin's excellent point that the symptoms must present an impairment in actual function.
And, as another note, plenty of other psychiatric conditions include distractability as a symptom!