I haven't looked into any research about this, but anecdotally I find this to not be true. Having peaked at 215 lbs. and ~12% body fat at 5' 11", (I'm now closer to 195 lbs. and ~10% body fat) I'd say that I'm in the top 1% in terms of muscle mass. I am often very hot. My theory is that because of the added muscle mass (which requires much higher food intake), I'm metabolizing food at a higher rate and thus generating more heat. I don't know if this is actually the case, but it's my theory.

This may not be the case for people who are fit in a more cardiovascular sense.

It often is, but I'm in pretty decent shape. I cycle regularly (my commute is 34 km one way), am not overweight and eat decently. For as long as I can remember, I've always started sweating very easily.

Is this actually true? I'm not calling you out, but I see it reported in comments all the time, but I've never read anything about it. I failed with a quick search.

Beyond that, this whole discussion just went down in another thread, but I'm like the parent post...I just sweat easily. Even when I was younger in great shape (4-6 hours of basketball daily) I would sweat quickly and profusely. I read that some percentage (~15% I believe) of people sweat more than others.

I'm 6'1" and a solid 215 pounds. I do powerlifting and Brazilian jiu jitsu. I get hot quickly. I've had training partners tell me that I "run hot", that compared to others, I feel like a furnace.