I thought only Americans mixed canned fish and mayo, guess it must be something we've sort of taken on from the British days. I think in the USA there is something called "tuna salad" on a lot of menus, and it's basically what you've made with some celery bits and few other things. It is a sandwich though, so confusing, and I'm sure plenty of foreign tourists have ordered a tuna salad before and were shocked to get the sandwich you made in this post.
Well, there's also something we call fruit salad back home, and it's about as far away from salad as one can get. Love the sandwich press, never had one but always wanted one after I worked at a cafe where I ran the panini station.
In the states, anything mixed with mayo is called salad 🤣