Up until around World War I pistol was as generic a term as handgun.
Colt and Smith & Wesson, as well as others, advertised revolving pistols and, as technology progressed, they advertised semi-automatic pistols, as well. S&W, with its single-shot target guns based on revolver frames, advertised target pistols.
As it has developed over the past 70 or so years, though, pistol has become somewhat generic for the semi-automatic, just as auto pistol or auto is now pretty generic for semi-automatic.
To say that a revolver is a pistol is technically correct, but it's really no longer common usage.
To say that calling a revolver a pistol is incorrect, though, is also wrong.