I have observed that most indicators on motorcycles (and cars/trucks as well) are significantly wrong: speed, distance, and on my Concours, miles per gallon, distance to empty, et al.
A few years back, Honda North America settled a class action complaint from car owners by extending the base warranty for an additional IIRC, 3,000 miles. My 2005 Accord was part of this settlement. It seems that the odometers were racking up distances significantly in excess of actual miles traveled. Hence, cars became out of warranty due to mileage sooner than they should have.
My wife's Ford Focus, my F-150, and my Corvette all register mpg readings on their respective on-board displays that are significantly greater than actual mpg as computed by dividing miles traveled by volume of fuel consumed.
I have become accustomed to it, and now just factor it in whenever I ride or drive.