the in Acrobat non visible elements mode is DeviceN, but the name of the DeviceN-color is "None" (in German: "Nicht drucken")
I am not 100% for sure, but if that alone does not force a disregard by previewing a RIP, i guess, that (the name "None") causes a mapping into the mode separation color (e.g. "All" is mode Separation color also...).
But "None" should expressly declared not to be reckognized by any RIP or professionel Preview interpreter like AcrobatPro and should expressivly not to be printed...
Remember e.g. a DeviceN-Cyan-object (mode DeviceN) in in a cmyk-file: you will not get a 5th separation/plate, it will be moved/mapped into the CMYK-mode/Separation-channel by RIPping...
But here it is "None"
May be someone had just called his own created spotcolor with that name or had klicked the None-filling in the color-palette, thinking that causes white/just not a filling or had changed it after export in PitStop or something else...