The post boil you measured 1.052? The gravity cannot go down from preboil, only up.
So the sample was higher in gravity than expected. Most refractometers will compensate for temp, but should be used at a particular temp for accuracy. The hydrometer needs to be corrected, but at a hotter temp than calibration points would need to be added.
Must be stratified wort and the gravity taken from an area of with a higher concentration of sugars.