In the corona, strong magnetic fields can make the temperature hotter than the normal 2,000,000oC. In the photosphere, strong magnetic fields seem to make the temperature cooler than the normal 5,500oC. There is no simple reason why this is so, so we'll have to leave it there. In fact, even solar physicists don't agree on how to explain these things. So if you're confused, don't worry, you aren't alone!