Only a guess, but I can imagine someone in the processing room (checking temps, adding replenisher) when the dip 'n dunk was up in the air between dips, and dripping something from their arm onto your film. Or as I've actually seen with my own reel/tank processing, perhaps a piece of solid matter temporarily adhered to the film, thus changing the development characteristic. Anyway, 11-year-old film is a crap-shoot.