Soldered test point on production board?
It looks intentional, either from the solder paste stencil or by hand at some point afterward. I doubt we will be able to figure out why it was done.
Adjustment can compensate for variations in several different components at once, and sometimes do a better job of it, so I suspect if they could have just used 1% or 0.5% resistors and gotten acceptable performance then they would have.
Modern designs often use EEPROM storage to save calibration settings, but usually there is a compromise involved (for example you might lose 20-30% of dynamic range to ensure that all units can be trimmed in despite production spread) and there is the possibility of  memory corruption &quot;bricking&quot; the device.
Trimmers can drift, but if the circuit is well-designed and the adjustment range is no more than necessary that is not usually an issue, assuming screwdrivers are not involved.