I do know that brewing tea with not-quite boiled water (70-80 degrees C) instead of boiled water 80-90 is recommended because otherwise the leaves go bitter.
Perhaps if they were using water fresh from the kettle the milk-first way was preventing the "scalding"
Bitter tannins are what you want in black tea, they're smoothed out by milk but a good cup needs to be grippy in the mouth. Black tea made with anything less than boiling water is usually not very nice, in my experience.
100% this. Which is why, as a Brit, my heart still sinks when ordering tea in most European countries: nine times out of ten you get a glass of once-boiling water to add a teabag to.
Yep, a proper cuppa needs the water at absolute boiling. 1000m above sea level is high enough that I won't even bother trying to brew a cuppa; it just won't hit the spot.
Milk is a factor. Weirdly for a country with a robust approach to pasteurisation, French milk is insipid.
In China, I couldn't even get hot enough water for coffee. The places I stayed offered water almost cool enough for a bath. I had thought I was clever, buying ground coffee in Beijing, but I might as well have carried a bag of sand.
Hey ho. Travel without privation is merely holiday.
I believe the point is to avoid overheating (any of) the milk, because that changes its flavour. For example, tea made with UHT milk tastes very different (and, to me, much less nice) than tea made with pasteurised milk.
When adding the tea to the milk, the temperature of the milk will never exceed the final temperature of the mix. When adding the milk to the tea, it will.
Perhaps if they were using water fresh from the kettle the milk-first way was preventing the "scalding"