This is a very interesting study, thank you for bringing this article to light! It makes me think that the lack of gravity coupled with the surface tension of water makes it harder for sweat to escape skin pores to the surface so that evaporation can take place.

I was also wondering about the ambient air temperature and what influence that might have on the ability of the body to cool by reaching an equilibrium. In the methods section of the study, they describe how the average air temperature in space was 23.6 degrees, compared the the 21.0 degree average for the earth baseline tests before and after flight.

This difference may be part of the reason for the increase in both resting and exercise temperature in space - the warmer environment in space means that heat is removed less rapidly by the skin equilibrating with the air temperature. The influence of this could easily be tested by running the earth-based experiments with the same average air temperature that is observed in the space-based measurements. It would also be nice to see a larger sample size where differences between genders could be considered. I guess this is an argument for further research into the subject!

Edit: I made an overlay from the included figure that normalizes the baseline temperature of resting and exercise to the pre-flight data point. This makes it a little easier to compare the differences between the two plots and see how space exercise causes a slight elevation in body temperature relative to the baseline.