As above, you have sat in a seat where a Seat Reservation label has not been applied
This is no longer your issue, but that of the other passenger
The other passenger is then entitled to sit in any other seat, and if no seat is available within 10 minutes to a minimum 5% compensation of the relevant fare for that journey
As mentioned already, ScotRail don't really seem too bothered about Seat reservations (except on the sleeper services)
The flaws in some of their (now rather out of date) seat plans has been pointed out but they do not seem interested
Ironically, they don't seem to have such issues on the Edinburgh / Glasgow - Aberdeen services
Furthermore, the staff at Aberdeen will try to apply all the seat reservations, even when boarding has commenced (due to a late arrival)
I feel for a passenger not getting what they paid for but I am not willing to vacate a seat which I occupied in good faith.
(assuming) All the passengers will have paid for their travel ticket
However the Seat Reservation is free