Caloojouc12 Yes, it is correct. Buchs SG is the border station and you can usually stay in the train when no engineering works are planed. I hope that your train will be rerouted, the new border station will be St. Margrethen, but your tickets will be still valid.
On the usual route Buchs - Feldkirch, you cross the Principality of Liechtenstein, a very small country between Switzerland and Austria.
It can be confusing, but separate tickets are often delivered for each country or in other cases for every train. It were to complicated to explain why. It could depend of the carriers, the laws or the different countries or commercial agreements between the carriers.