Probably used to have something else in that spot and the shelf fillers shoved it in there without changing the ticket, happens loads in our branch. We have some trays of pate in for 19p at the moment I think so maybe the ticket says similar things? I was a bit cynical about the mushrooms myself, and it's a typical 4% meat effort so not great, but like you said they're ok to eek out the fancy stuff. I usually feed one tin per day with other things, as opposed to the 3-4 it reccommends on the tin.