The reality here is that the word “tea” is a much abused thing.
What the UK (and Ireland) drinks is (largely) a mix of Indian, Sri Lankan and Kenya teas. Which typically has milk (not cream) and some sugar added, but not always. This tea is relatively strong, thus milk works with it. Some people add a lot of sugar to it (a joke often being builders having very strong tea and 12 spoons of sugar)… Most just have a single spoon or sweetner.
Some in the UK, and a lot of the rest of the world, drink herbal infusions containing nothing from the tea plants at all, and call that tea. All those fruity and herby concoctions.
The rest of Europe, and thus a bunch of the US (being made up from immigrants), drink a weaker tea blend, typically with lemon, and perhaps with some sugar. Being weaker, it doesn’t work well with milk added.
I’ve lived in Belgium, I used to bring my own tea with me, the tea there isn’t strong enough to make a British cuppa.
The scientist is probably referring to either the latter, and possibly the non-tea versions of tea.
But since Brits drink so much tea, often over coffee and soft drinks, they can consume a lot in a day. And thus feel strongly that their tea is the only tea.
The cultural equivalent would be the Italians reacting to someone in the US telling them how their weak instant coffee can be improved, by, I dunno, adding chocolate to it. They’re disagreeing about two different things.
But hey, nuance is not possible in the modern internet. Just a place for an argument, never understanding.
(Chinese tea fits into this conversation somewhere. I quite liked it, the one time I had it free with one of the meals, but it’s closer to the US version I think).