Not airborne, but spittle born, which to someone of the speech modes of President Trump, is likely seen as the same thing.
President Trump is a man who thinks in terms of simplified basic function, not precise technical distinctions, which for a politician is fine and understandable.
I've seen allot of people arguing that the mask do no good because the size of the virus is smaller than the particle block size of common cloth filter mask. But in the technical analysis of mask effectiveness, it not expected to block an individual virus organism. A single virus organism on its own dies within a few hours under ideal conditions, and quicker than that in most conditions.
The operating principle of virus transfer is a blobs of spittle projected by a cough or sneeze, and the saliva medium of transmission is more viscous than water, and the air speed of the cough or sneeze is highly variable. The airspeed combined with viscosity sets a gaussian distribution range of droplet sizes, most of which are well within the capture range of common cloth filter masks. Additionally, the smaller the droplet, the more rapid the velocity drop off from air friction and the short the projection range of the ejecta.
These are all well studied and understood principles of hydro and aero dynamics, which have been used for over 100 years in the applied science of chemical and germ warfare weaponization.
The upshot of it all, it that cloth masks do provide a modest measure of protection, if worn and handled during removal and cleaning, properly, which most layman don't really know how, or bother to do with the needed discipline. And it really only works if the sick person, who doesn't know they are sick yet, is wearing the mask. The mask has next to zero effectiveness when worn by the healthy, as yet, un-infected person.
Sick people are usually somewhat disoriented and clumsy, and their ability to correctly wear, dismount, handle and cleanse the mask, without effecting others, and is significantly reduced over a trained, self-disiplined and healthy person.
So, Masks are not likely to be a huge factor in preventing spread, but, every little bit helps.
Was President Trump wrong when he said "Airborne"? No. Not when considering his broad and uneducated audience and the need to emphasize the danger is real, and can leap across an open space between people.
And if Trump had attempted to use the language I have in the above paragraphs, no one would have gotten any message!
President Trump gave a good, effective message for passing the needed caution and concept, considering the audience, media and venue. Good Job Mr. President!