Thanks for sharing this Robin. When I first looked on the AAVSO database there were no recent IR measurements, it is great these have been added.
I agree this implies a cooling rather than a change in total luminosity (bolometric).
It is possible the star may have expanded a little rather than contracted as I have seen some saying, to explain the cooling. Though that is pure speculation on my part. A more detailed analysis of the existing data and ideally additional spectra in the IR would help to tie down the change in bolometric luminosity and temperature, to then understand if it has changed size.
Cheers,
Andy