If you look at the specification, and always provided the shunt is temperature stable (RUG-Z...), the accuracy of these DCC bridges is extremely high. See also data sheets, sub ppm. So the digits shown on that shunt could make reasonable sense (data given with 0.1ppm res.), again provided this specific shunt is stable. The latter may not be the case with this one. These bridges use a SW, and typically a calibration consists of say 10 measurement cycles, with 10 measuremens each, generating an average and calculation the standard deviation, which is then transferred into the appropriate measurement uncertainty stated on the shunt cal doc. Some cal labs using these bridges here certify in the 2ppm range uncertainty at 1mOhm, one additional digit is given most of the time, brings you to 0.1ppm resolution. More of a problem is the aging drift. This may e.g. be a couple 10ppm pa with a RUG-Z not operated at high currents frequently, and much more under heavy load conditions. Also the load current applied strongly affects the measured value.
And of course with a simpler setup (DMM and current source) such resolution does not make any sense.