Chai masala variants may be boiled that long or more – they do contain black tea, but also spices (where the boiling is needed, to extract the flavor from whole spices). The tea decoction this produces does contain all of the bitter compounds, sure – but it is mixed with spices, diluted generously with milk and sugar, and becomes a palatable drink that is nevertheless very different from the coolly and weakly brewed variety you seem to be familiar with.
In fact, it is even possible that the tea was plain black tea, brewed very strongly. Served with plenty of milk and sugar to balance the bitterness, milk tea is a cultural variation. Think of it kinda like coffee, if you want – it is bitter, but it is expected to be – and the tea can be doctored to make it work for the drinker.
Tea can be served in lots of different variations, and none are more correct than others – just like some teas are brewed very light and almost flavorless (japanese green, and 15 seconds per brew), and others are brewed to death and sweetened to balance (southern style sweet tea), some are served with milk, sugar, or lemon, and still more are served with salt or butter (tibetan). Boiled milk tea or chai are brewed to death, to extract all the flavor, and served sweet and milky to balance the strength and bitterness – and a weakly brewed tea would be tasteless and vanish in the expected fixings.