I have a husband who is a fussy git at home, examples would be only likes spaghetti or linguine, will not eat shells/spirals. Only likes onion cooked in stews, not fried. Does not like melted cheese or creamy dishes, but will eat lasagne.
Does not like margarine, brown bread, lamb, most fish, shortcrust pastry to name a few.
However if we went out for dinner and the host had asked beforehand "do you like spag bol and garlic bread?" he would say yes, and we arrived to find it had been made with pasta spirals, grated cheese on top, with brown garlic bread, he would eat it without any complaint.
If we are in a restaurant he would never order something he hasnt eaten before, but if he was offered it at someone house, he would have a taste to try it.
That to me is how a "fussy/picky" eater should behave if they are a guest.