I checked the New Taipei City Public Transportation website as you suggested, and in the dynamic map it is only referenced in the "Go to Beitou" direction, and not in the "Return to Tamsui" direction  [https://ebus.gov.taipei/Stop/RoutesOfStop?stopid=2516302540]. However, There is a bus stop sign visible in Mapillary: The bus stop in question [https://www.mapillary.com/map/im/2858292731086622] - The known and mapped stop [https://www.mapillary.com/map/im/772077843476236] - Both signs visible [https://www.mapillary.com/map/im/797579027542084]. I also found the transit map for route 631, and it does not specify that it is a "one-side" or "two-side" stop, but a "staging area"[https://ebus.gov.taipei/MapOverview?nid=0400063100]. Let me know what you think. I can remove the note if necessary. 