Timo said:
Hmm... Kirk readily gave Starfleet uniforms to civilians: Charlie Evans (although his old-style pullover was probably Antares fare), John Christopher (not Starfleet, even if not strictly civilian in his own opinion), Khan Singh...
But that practice seemed to stop in Picard's era though. It was not uncommon to hand out combadges to civilians like candy, but uniforms seemed like a big deal.
In Kosinski's case, his association with Starfleet might be that he indeed works for Starfleet but only as a propulsion specialist and that his insignia is unique only to such special personnel. As a hologram specialist, Lewis Zimmerman might have worn a similar insignia at one point...