I don't see why get upset. You know your rabbits are ok, so no reason to get upset by what they say.
If they were getting sick a lot, footsore, not eating well, dirty, then that would be different - but the British way of keeping buns still might not be appropriate over here.
However, it really IS a good opportunity to learn how they keep rabbits over there and why - exactly what their reasons are.
What could be different? Well, I think for one thing, the wire products over there might be really bad on their rabbit's feet. So it might be a much less viable option over there. There could be a lot of things like that.
I also know the climate is really different there. There is an awful lot of damp rainy weather there, and usually without the hotter and colder extremes we have. So they may have to keep their rabbits under a very different system. I would imagine mold and fuguses are a lot more of a problem over there than in Nevada. Parasites too. I think there are actually quite a large number of parasites that can damage baby bunnies in the British Isles. They have diseases of cattle there too - parasitic diseases, that I don't think are a major factor anywhere else (is one louping ill?)
And things that don't even come into play in Brittain would be crucial in Nevada - heat stress, for example, they have many more 90 degree and plus days in Nevada. I didn't pick Nevada for any particular reason other than it's very different climate there than in Britain, and to say that what works in Britain might not address a lot of the USA unique problems.
THAT - and grazing their bunny babies might be an awfully lot different proposition there than it is here. So they may have to not put any babies on grass. I know the grass pastures are totally different for horses there, so the lawns may be very different too.
I think the best thing to do is to thank them very warmly for all their help, and store it away as useful information, but maybe just not applying to your situation right now.
Don't tell that that, though! Just be grateful and say they've given SO MUCH helpful information! THAAAAANKS!
It's interesting, though, trying to figure out why people do things differently. Tradition? Habit? A difference in environment? In the animals? I know when I was in Belgium folks there told me their baby bunnies can't be grazed - I can't remember why - but they were these gigantic rabbits, and I think their care differs from other rabbit types. I think that the problem was the parasites they could pick up and concerns about a low natural resistance in that breed at certain ages.
It could be something as simple as Brits saying 'bunny' and meaning 'newborn' and going off without you two even realizing you aren't talking about the same age bunny at all.
OR....they could have simply assumed you were in Britain....
Even in the same area, I can see one neighbor that keeps their horses very, very differently from the folks next door. So some of it is going to be the traditions that person has learned, and their goals, and what things most worry them. Differences in keeping animals can have a lot of different reasons behind them....and tradition, what you're used to - that can be a big big part of it. Or just experience - a friend of mine doesn't even allow people in her barn with cigarettes in their POCKETS - and she is always screaming frantically at the help to cobweb around conduits and electrical outlets - her horse died in a fire....