So bluetooth tethering basically? Also, maybe that way so users can’t use a vpn client, unless it will still work with that app in the middle.

And off topic, those videos with that music reminded me with those safety instructions videos they play on airplanes :)

No, bluetooth is only used to let the network know that you are on the train. The big Swiss mobile carriers work in cooperation with the railway and will automatically use this attestation to basically give you free unlimited data for the duration you are on the train.