Yes, and airborne is extremely unlikely.
Your example would be like saying that AIDS can evolve and spread via the air.
The ebola virus requires direct contact, fluid to tissue.
The thing that makes containment difficult, is that in its acute and infective stage, the patient sheds billions of virons through profuse perspiration, projectile emesis, and explosive diarrhea. Those in direct contact have a distinct challenge just getting out of their protective suits.
The virus is not shed until the acute phase begins. Therefore, passengers on the plane with Mr. Duncan were not at risk; similarly, we don't need to fear public exposure with unknown "carriers"