"White sugar is for tea, while brown sugar is for coffee." Is that true? Why is it so ? Thank you!?

White sugar is just sweet, it has very little flavor other than adding sweetness. So it doesn't interfere with the delicate flavors of tea. Brown sugar has some flavor as well, the flavor of molasses, the 'raw sugar' flavor. Someone thinks that goes better with coffee. But a lot of people would rather have white sugar in their coffee.

Also I like honey in my tea because it does have some flavor beside just being sweet.

White sugar is for both tea and coffee and brown sugar is used for cooking.

I use white sugar in coffee

No sugar in my tea

I usually drink pure loose leaf tea, without adding any sugar, to enjoy its original taste. For fruit tea or herbal tea, the white sugar will make them tasteful.

I worked in a coffee shop and I have never seen anyone put brown sugar (save for sugar in the raw I guess, which is not really the same) in their coffee

Not really.

back in the day when I used to use sugar, I would always use brown sugar for both tea and coffee. To me it had a pleasant caramel flavor.

No, it isn't true. Some people may prefer one kind of sugar in a certain beverage, but that doesn't make doing that true. It's just their preference.

'True' is what you'd say about something that's universally known as a fact, like you'll get wet if you stand in the rain.

Not necessarily. It is a preference.