Because if LE had been able to rule that out, they would say so. They would announce who the person was ("neighbor with a colicky baby, who's been cleared"), which is what they usually do. IIRC, they have specifically said they have not ruled it out.
This has been asked and answered several times on various threads. That's why it is still being raised. The fact that ANOTHER person has come forward is also strange, and LE has not ruled his sighting out.
Considering that other person waited a week before contacting LE, I have no idea how LE is supposed to rule his sighting in or out.