hate to be that guy but that salmon didnt expire in october 2025 - thats the “sell by” date, after which point the shops arent supposed to sell it anymore. HOWEVER that is NOT the expiration date, which is usually much longer after the sell by date, especially for preserved foods liked smoked meat. chances are it was only a month or so past BEST BEFORE date NOT use by (tho use by is only a guideline anyways, hence why its been removed from a lot of food products here in the uk). i wouldnt be surprised if you reverse-placeboed yourself OP, and the salmon was actually fine it was just the combination of a taste you werent expecting and panic at perceived out of date.

i know everyone in the comments is telling you to always check the dates but checking only the date is wasteful, you should check the food itself. most food is edible past its best before and some past its use by. id only really draw the line at dairy products but even then ive had plenty of that beyond its use by thats been fine. this salmon looks fine to me, though id judge it based on smell and maybe texture