We apply a thin plate spline (rubber sheeting) to the GCP locations so the error should be near zero there. So those numbers are a bit high but if you are measuring points away from the GCP they are reasonable.
We do not make any morphological corrections to the initially computed model. Offset and/or tilt is applied to minimize the elevation error at the GCP locations but there is no correction for barrel distortion or swelling.
To check the values you can simply mouse over the location in the Maps Made Easy web map to see the elevation value. Or you could use the DEM itself.