Most likely one of the mid-haul A321s has had a tech problem and either the only available aircraft has been a short haul A321, or someone's decided that it'd be cheaper to pay out goodwill compensation to the passengers that it would've been to replace the aircraft with a spare higher-capacity long haul frame. It'll certainly be cheaper (and IMO better for everyone) than cancelling the service and paying out accommodation/rerouting/EU.261
I'd put in a polite-but-firm complaint about the lack of catering and IFE, they're almost certainly expecting them from the majority of passengers who flew on that flight.