The concept of "center of mass" in the form of the center of gravity was first introduced by Archimedes of Syracuse.
As far as the center of an orbiting system is concerned, the Antikythera mechanism is an ancient Greek hand-powered orrery, and the oldest known example of such a device, used to predict astronomical positions and eclipses for calendar and astrological purposes decades in advance. It materilize with gears the, then in use geometric models, based on epicycle with equants which are figures similar to your nice illustrative gif.
Similar, with the exception that the big circle (the sun) and the small circle (the planet) were exchanged. It was not because the greek did believe that the sun was orbitiong around the earth [that's a meaningless question for computation], but because it was a good way to take into account in the model the difference of speed (2nd Kepler law) with gears that cannot be elliptical. So there were no reason to make all the equans equal, and make them equal to the sun-earth distance, as Copernic did, simplifiying at cost of accuracy.
In antiquity, accuracy was much more important (for navigation, for oracle, and for religious feast) than explanation. So, if the epicycle, deferents and equants were of common use by Ptolemy, and if Archimedes did estimates the weight of the celestial bodies, it was not before the distinction between Weight and Mass, done by Newton, that the equant could be identified with the center of mass of an orbiting system.