More specific to the answer by Redoute is that the two points are projected to EPSG:32619 (WGS 84 / UTM zone 19N), determined by the utility
_ST_BestSRID(geog), which have transformed coordinates:
- ex1: SRID=-32619;POINT(414639.538157217 4428236.06463343)
- ex2: SRID=-32619;POINT(329274.505728464 4429672.97311587)
These points are buffered by 10.0 m (in Cartesian space), and projected back to geographic coordinates, where a geodesic area is finally calculated. The differences are due to distortions of UTM Zones on an ellipsoid of revolution (aka spheroid). The calculations are generally better when they are near the middle of the UTM zones, and worse when they are near the boundary of two zones (e.g. Calgary).
A very good calculation for the buffered point is 312.3 m².
And the area for a perfect circle with radius 10 m in Cartesian space is π10² = 314.159265358979323846264338327950288419716939937510... m².
The area of a perfect circle will always be bigger than the area from ST_Buffer, since ST_Buffer makes a polygon with the curved edges cut off.