The same thing happened with an MD-80 in Spain some years ago, and the circumstances look similar. Mainstream carrier (it was Spanair then) has wet-leased in an aircraft, including the dispatch of it, from a foreign carrier (that was from a Scandinavian charter company), so the crew did little/no PA and local cabin crew did it all. That flight, from Madrid, went south to Valencia instead of north to Santiago. The crew had just done a Valencia round trip, and their paperwork just had them down for a second one. Meanwhile all the passenger-facing side has them announced as going in the opposite direction. Everything of course was flightplanned and organised correctly by the crew for where they were told to fly to, it was only when they contacted handling on arrival they found they were not expected.
Strangely, on that occasion it was IMC throughout and the pax never noticed. Today it's been pretty much CAVOK for the last two days. Did none of the pax query the routing when in flight ?