Interesting angle. I agree with the placement of the tack in the lower third, at least that’s where I wore one. Also, a tack seems to have more options for customization as in a logo, etc. Mine would not point directly to me, but would be pretty specific to a certain function. So yea, a pilot’s tie could be possible. Cooper may very well have removed the tie tack if it could identify the owner or at least narrow down the field.
Pilots and plane crew are constantly on the road and staying at hotels. Any of us who have traveled a lot know how common it is to leave things behind. There is nothing that says Cooper didn’t find that tie.
I still think he may have left the tie on the plane on purpose, as a symbol or because he didn’t care.
Edit. Looking on eBay for old tie tacks, I see a lot of military, railroad, and airline. I think a lot of corporations probably had their own.