Oh, my, no, especially the sort of handgun commonly chambered for a .223, such as a Thomson Contender or the old Remington XP or even a custom jobby. These typically are scoped and quite capable of 2 MOA or better.
Personally I suspect a carbine, myself. Many of these have extensible stocks and short barrels and would be ideal for vehicle employment - that's what they're designed for. But it could be pretty much anything - I don't know of any .223 rifle or pistol that wouldn't be perfectly adequate at 100 yds if properly maintained and employed by anyone who practiced.