A measurement system can be accurate but not precise, precise but not accurate, neither, or both.
Accuracy would be in reference to a measurement system, measuring the value to the measure of "true" value. Precision is the measurement of accuracy, more so the ability to reproduce the same test with the same results repeatedly under the same conditions.
In absolute terms, your comparison is not valid at all because your not comparing rifle to pistol using the same methods, you are estimating based on results from 15/25 or 50 meters what the actual 100 yard results would be and not even considering the other factors that come into play IE ballistics, windage, humidity, speed, gravity... your essentially ruling out all concepts of ballistics with it. This completely undermines the concepts of the accuracy and precision.
Precision can be stated as being able to shoot an 8" gong at 180 yards, if you do that consistently with a glock than yes it is a precision instrument. Your sights being on the 10 ring, and putting a bullet there is accuracy, your ability to put 10 bullets in that same x ring is precision.
Minute Of Arc is an actual "valid" unit of measurement, it is extremely accurate and precise because it has an established criteria. Applying it to a distance of less than 100 meters is simply irrelevant, especially when talking about the instrument. Handguns were never designed or intended to take shots at 200 and 300 yards, just because they can doesn't mean we should start measuring them in c-hairs. The results become to vast to be accurate and precise, therefore they are not valid and can't be MOA. If a pistols test was to put 5 shots in a 1" group at 100 yards, and it can do this repeatedly, then you can claim MOA.