One wonders if there was an organisation Snafu between Swiss and their flight contractor Edelweiss. This flight is coded WK for Edelweiss, normally operated by one of their A320s. Although owned by Swiss, they have a separate AOC and brand image. However, just one of the flights to Bilbao a week, the one in question, is operated by Swiss themselves, with a smaller A220, although still coded for Edelweiss, in a sort of reversal of the more common approach where separate independents operate for the mainstream brand. My hunch is there are separate dispatch operations for two separate AOCs, and between them something got dropped and the baggage handling was never booked by either party. Seen this sort of thing before.
One hopes the FOCA in Switzerland will look at the flight dispatch, whether the bag load was incorrectly shown, and whether the commander was informed they had been left off, or just accepted the paperwork with bags = 0 shown.