The site can only work with the timetable data, which ScotRail have evidently entered incorrectly (or they are planning to remove first class!).
I'd recommend complaining to ScotRail and making it clear that the eNRT (https://www.networkrail.co.uk/running-the-railway/the-timetable/electronic-national-rail-timetable/) shows it as being standard class only, and asking them to either edit the data, or confirm first class is declassified on the service.
I'd recommend complaining to ScotRail and making it clear that the eNRT (https://www.networkrail.co.uk/running-the-railway/the-timetable/electronic-national-rail-timetable/) shows it as being standard class only, and asking them to either edit the data, or confirm first class is declassified on the service.