They could have taken them off us and fed them to their dog or something if they really were that suspicious of furrin food.
My suggestion would be for your missus to next time offer something more neutral. Like a packet of hobnobs maybe

In our first year here my 5 year old's birthday party fun was dampened when it was found out Belgian kids have no idea what jelly is. And most of them didn't even want to try it!
Me I got no problem with dumplings but for years I worked in seaside pub with a function room. Once a year we would get a booking that would bring us a coach load of Caribbeans from London for a day trip. They would have the arrangement where they had use of the kitchen and 4 or 5 would cook for everyone carribean style. The barstaff was always invited to tuck in when they trickled in for their fill after a day at the seaside but it took me years to trust the goat curry

The landlord had lived in South Africa for years and he was cool with it all and tucked in year in year out. Glad I eventually did though.
I thought it was unspeakably rude. The sad thing is that it probably would be quite a common reaction in the UK
You are generalizing.
England is a class society.
Working classes in England don't keep up appearances unless they have to.
I sort of got this smile on my face as I can see the situation in the other flat after the bloke shut the door. Bet he got a right bollocking over being rude which is probably why she rang down and tried to make up for his rudeness.
Not that she did a very good job

.
I repatriated 2 years ago after 22 years in England, more than half a lifetime. I see my country of birth as an elitist society. The classes are there but they are expressed differently. And there is this societal pressure to confirm to the appearances to pleas all
Belgium is very much a middle class in apearance but the people have not the integrity or any sense of ethical thinking of their own or beyond that what the media feeds them and now i'm generalizing too
I often think it's unsurprising that immigrants find it hard to integrate when this is our general culture.
People emigrate for different reasons. Many of those coming to the western world are economic immigrants and have no initial intention of ever assimilating into the culture they are immigrating into. They only leave their own countries because it doesn't provide them the opportunities they believe they will have in the west.
I would call most westerners that emigrate cultural refugees, most of them leave because they are disillusioned with the society they live in and when they arrive in their new countries most have a rough idea of what they letting themselvs in for in the cultural sense to some degree leaving them more open to the idea of integrating in the society that is.