Let's use some basic logic here: What is the hottest part of the CPU? The cores. Therefore is it possible for the temperature external to the cores to be far hotter (or even as hot as) the cores themselves? No. Therefore one of them is wrong, and it's likely to be the CPU temp. Remember that CPU and core temperatures are dependent on ambient as well, and you haven't told us your ambient.
I suggest reading this too: http://www.tomshardware.co.uk/forum/221745-11-sticky-core-core-temperature-guide