8bjtgame, if you go to a BBQ at someone's house, don't you usually have a range of salads or side dishes to go with the meat and bread? Otherwise it's just a burger in a bun or a sausage or piece of chicken. It doesn't feel like 'going out' and having a meal. Yes, if you have a BBQ at home it's usually pretty simple, but when you've got people round, I'd usually provide some other bits to go with the meal or that's where others often come in with bringing a dish at a BBQ.
Common side dishes at a BBQ could be potato salad, a pasta salad, a rice salad, perhaps a green salad or something like tomato mozarella platter. There could be corn on the cob or other vegetables done on the BBQ too. In my mind, there's a table of these side dishes which also has bread for the meat and dressings/sauces and maybe drinks. People take their plate to get their meat and then go and help themselves from the food table to side salads etc. Later puddings would be out there. This is a big BBQ for perhaps 12-30 people. If it was for under 10 I'd probably have everyone sat round the garden table and the side dishes might be there and someone would bring the meat to the table as it was cooked. But again, there no wrong or right.
But in my mind, BBQ especially lends itself to people bringing a dish...usually cold. I love a different salad like coronation chicken or one of the special pasta salads my friend does...I can easily have a spoon of those next to my meat from the BBQ and they don't seem out of place to me...but whatever you want to eat.
To be honest, unless it's a BBQ or some kind of outside summer picnic/buffet type thing when most dishes can fit in, if I was bringing or asking spoke for something it would be a desert as it's easy to have a couple of different ones and doesn't clash with other parts of the meal.
I can see a fish pie doesn't really fit with BBQ, which is why I wonder if it was a gift for later really,meat her than intend to be eaten alongside BBQ. However, even if a dish seemed quite odd or unsullied, I wouldn't consider it 'rude'. Perhaps the person brining it forget it was a BBQ. Who knows? It was a kind gesture to bring something, that's allI'd think and not dwell on it.
One other thing to realise is that for some people, often younger people hosting can feel really expensive. One way to be able to do it more often is to ask people to bring things. Not having to pay for a pudding or the booze can cut the cost considerably and if it's a way of doing things amongst a group of friends, seems fine. The idea that you can only host if you provide absolutely everything, in the same way some people say no one should host a wedding unless they provide a free bar all night, just seems very rigid and a failure to appreciate the different circumstances people are in.
Some of the best nights I've ever had have been with groups of friends having 'bring and share' meals that were very informal and cheap. Again, it's all about the company and being welcoming and hospitable rather than 'rules' about what you must and must not bring.