Yup, 49cc is just the displacement of the engine.. the volume the piston displaces in it's upward stroke...
Other factors determine horsepower (again there's brake HP , wheel HP, etc.) or engine power like the carb, or fuel injection, cams, valves, engine weight, ignition, etc. etc. etc.
A 1600cc car engine with single overhead cams, 8-valve, twin barrel carburetor has a lower horsepower than a 1600cc with double overhead cams, 16-valve, double twin side draft carbs.