Yes because you bought the ticket from ÖBB so they are responsible for refunds too.
It's still a Train operated by MAV (and you also can buy tickets from them directly) and the ÖBB Nightjet Website explicitly tells you:
"Der Umfang und die Qualität der Serviceleistungen in einem EuroNight Zug und das eingesetzte Wagenmaterial weichen vom Angebot des ÖBB Nightjets ab."
"The scope and quality of the services in a Euronight train and the car material used deviate from the ÖBB Nightjet offers"
Okay. Isn’t it a technicality though? In the end of the day, ÖBB sells this through their website so they should stand behind it. It’s too easy to sell anything and everything and say “caveat emptor, it might be total shit or maybe not but in any case I’m only here to take your money.” See Amazon and how happy people in general are with their comingling problem.
That’s my opinion anyway, feel free to have your own.
No it's not a technicality?
I can buy tickets from Deutsche Bahn for all kind of European Train Operators, including ÖBB Nightjet. It's just a nice service to have a unified booking system
So no, you didn't rode an ÖBB Train