I recently spoke with an FAA POI about this very subject regarding my flight times. As their Letter of Interp was given to them, “commuter airline” refers to an operation as PIC where utilizing the ATP license is required AND/OR the “commuter” holds out to the general public for flights that are scheduled in advance (I,e: pax can book a ticket from A to B at least three mos out).
My part 135 commuter time is considered on-demand, read cargo, and therefore does not qualify as time that will meet the FAA definition of commuter.
That’s my experience on the subject but it may very well differ with each FSDO. Good luck.