slow roasting; internal temperature higher than oven temperature
Besides a unit of measure mistake, It is possible to get this kind of read-out, even with accurate thermometers.  Though the roast can not be hotter than the oven, no more than a bowl can be hotter than the soup it holds.

Possible causes:


Oven temperature was read after the door was opened (cooling the air inside).
The dual read thermometer's tip is poking through the meat and actually reading oven temperature while the oven read portion touching the meat and actually reading meat temperature (so, reverse read).
Some ovens can cool down faster than the food inside (generally not a good thing)
If the roast was partially frozen before cooking, and the oven temperature sensor is close to the meat, the temperature can seem reversed for a while.