... with windows with a better R-value than walls ?
--- i'm skeptical...
You should be skeptical, Davide!! Something is clearly not right. Windows are about 20% reflective but all of them at that angle could be reflecting the same cold sky.
I think the interior temperatures of the buildings were different. I have R=10 windows and even they are warmer than my R=45 walls!
As the image below shows, we can make windows appear pretty much an... Interior temps in this image were all the same; the difference is what is being reflected, cold sky (top), warm surroundings (bottom) or a mixed background (middle).
Is the emissivity difference between the glass and the wall making a difference too?
It is certainly possible as I no longer have the exact specs for the older windows. My belief, however, is that exterior surfaces of both old and new glazings are uncoated so what we are seeing is related only to the difference in actual heat transfer.
For the other image (3 windows stacked), all three windows are identical. The difference in "apparent temperature" is entirely due to differences in the reflected background temperatures.