Disclaimer: I'm writing as a professional chemist, not piano technician.
To my chemist's eye, this shiny, globular corrosion has all the trappings of acid-induced rust. Some substance was applied specifically to the top part of the pins - the first two hunches that come to my mind would be
1) an attempt to chemically blue the pins (as opposed to applying bluing dye), or
2) an attempt at removing previously applied chemical bluing (which would typically require some form of acid).
I am surprised to see the coils and lower parts of the pins in such good shape. Whatever was applied, it must have been done with quite some care.
I haven't used these tuning pin / coil cleaners, but if they are somewhat abrasive, I think that spinning them (dry, for starters) on the pins could restore the pins to a passable state.
(credit: Schaff Piano Supply Co.)