Of course they could have and this has led to people being removed from the train by the federal police (which is extremely costly as the German Bahn charges one for the delay costs and the police also charges one).
When you reserve a seat it means you have the right to use that reservation for 15min after the train left the station and not be moved from it when you have a taken the seat.
The reservation even is void if you decide to sit in another seat before claiming your seat or go to the restaurant before claiming your seat.(Afterwards it’s different)
And of course you still have to have a ticket for the class/train. By your logic you could have simply reserved the seat for 4€ and then used no ticket at all - which is of course also wrong.
BTW: It says you need a valid ticket for that class in bright red letters on the webshop.
TLDR: You could have been removed from that seat and it would have cost you a lot of money if they did.
Of course they could have and this has led to people being removed from the train by the federal police (which is extremely costly as the German Bahn charges one for the delay costs and the police also charges one).
When you reserve a seat it means you have the right to use that reservation for 15min after the train left the station and not be moved from it when you have a taken the seat. The reservation even is void if you decide to sit in another seat before claiming your seat or go to the restaurant before claiming your seat.(Afterwards it’s different)
And of course you still have to have a ticket for the class/train. By your logic you could have simply reserved the seat for 4€ and then used no ticket at all - which is of course also wrong.
BTW: It says you need a valid ticket for that class in bright red letters on the webshop.
TLDR: You could have been removed from that seat and it would have cost you a lot of money if they did.