And the scale is calibrated such that as long as the scale is not moved then the reading does give the mass of the object in pounds.
If the scale is moved then the reading changes to X. so it is giving us a force that is the force we would expect from a mass of X on the surface of the earth.
Now times change but traditionally we had to differentiate between the force that was produced by a mass of one pound, ( lb f ) and the mass of one pound itself.
Without the subscript f then we are dealing with mass not force.
So your scale reads 10 lb f ( 10 pounds force or if you prefer the force of gravity that you would get on a ten pound mass on earth )
But the dumbbell does have a mass of 10 lb and it would continue to have this mass no matter where in the universe it was taken.
Many of these anomalies were addressed within the metric system and have been retrofitted to the imperial system. Hence the unit of the slug.
But it is not the only valid unit of mass.