I suspect this was done using one of the dreaded digital techniques, but it reminds me of work done using the POP solarization process described in Petersen's Photographic, January 1977 edition.
The basic idea was to soak a sheet of paper in developer prior to exposure. The wet paper was then given two exposures - the first was short and bright, typically with the aperture wide open. After 20-30 seconds, a faint image would appear on the paper. Then, a second exposure - longer and with the lens stopped down - was required. The partially developed image from the first exposure would hold back light from the second exposure, whle the second expsoure would complement the first both as additional expsoure and as a partial solarization exposure. The result was quite striking - at times it looked like a normal print, while in other instances it looked solarized. The process would produce detail in highlights that normally would be totally blown out, white mackie lines at the boundaries between highlights and shadows, and some of the most beautiful silvery midtones I have ever seen.
The process required the use of high contrast graded paper - Agfa Brovira #6 (when it was available) or later #5. I did a number of these that were successful, and I also tried it with VC paper with no success.