Apparently, they hat do go to pick up pax in Bilbao to get back before Zurich closed for the night. I can understand that offering to deplane would have cost additional time, and if at all, should have been offered a little early, together with an announcement that they were likely to leave within 20 minutes without bags and now was the time to get off if that was too much of an inconvenience. I also do not see why someone would have to break the news on the ground. What's the problem with doing a PA on the plane?
Just last week, flew LH Cityline DUB to MUC. Delay of 45 minutes, later extended, was announced early on. Once boarded, the captain said something about issues with baggage handling in Munich. Well, got into MUC about an hour late with most of the terminal and baggage claim already shut down and had to wait for another hour for the first bag to appear. Nobody bothered to inform whether bags had made it all.