I'm pretty sure that you're right. AMD motherboards have been using thermal probes in the empty space of the socket for ages, and they've <i>always</i> been a very unreliable source for your CPU temp. So I'd just go with the diode temp and completely ignore that unreliable socket temp.
Of course, I could be wrong. I don't have Motherboard Monitor on an AMD platform so I don't know for certain if 'diode' is the CPU's diode and 'socket' is the sensor in the socket. Maybe 'diode' is the thermal diode mounted on the mobo and 'socket' is the temp from the CPU in the socket. It'd be silly to name them that way, but I wouldn't put it past them...
<font color=blue><pre>If you don't give me accurate and complete system specs
then I can't give you an accurate and complete answer.</pre><p></font color=blue>