I don't know that you're an anomaly...but perhaps in the minority.
Many folks with MS find that our internal thermostats are "broke" -- the thermostat that controls our "core body temperature". So we overheat very quickly and easily. I'll use myself as an example: I used to sweat a lot as a kid. Once the MS took hold, I stopped sweating. Sweating is the body's way of cooling itself -- you sweat, the water comes to the surface of the skin and evaporates, the evaporation is a cooling agent, so you are cooler.
I don't sweat. So if I'm in the sun, especially in humid weather, I overheat in as little as 20 minutes or so. Any sweat that does come to the surface doesn't evaporate in the humidity.
A very long time ago, one doctor-performed test for an individual to determine whether she had MS was to put the patient in a tub full of hot water...let them set there for awhile, then tell them to get out. Generally the patient would be unable to do so: the legs would not hold up the body, overall weakness would affect other muscles. If the patient indeed couldn't get out -- she'd be diagnosed with MS. So it's not like I'm making this (my comment you referred to) up! And it's not a side effect of the interferon....but more commonly a symptom of MS.
I can't take hot showers. If I stay in the shower too long, it's a challenge to even transfer from shower seat back to wheelchair. I'd never even consider a hot tub, or any tub of water for that matter. I know I'd not be able to get out. I live in Wisconsin, plenty cold in winter. My house thermostat is set for about 64 degrees, and I have central air in my house. I go barefoot (well, I do wear socks) all year round inside.
When I DO get overheated, the first thing that happens is my face flushes bright red. My legs weaken dramatically. Then I start to get dizzy. If I don't retreat to the cool air right then, I'll start to get disoriented, and eventually would faint. So on hot days when I know I have to be outside I carry PLENTY of water, cold packs, wash cloths that I can wet down and drape around my neck or even just plunk on top of my head. I wear a hat, carry a fan --
actually generally I try to avoid going out at all if the temperature is much above 75 degrees.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....