It was not, as it were, about being formal. More due to how they were both raised. Something that their uncle had instilled into the both of them. The moment that his brother holds out the tea he takes it and moves into the kitchen to put the kettle on. That, to him, was an interesting invention. Even if they still did things in the way of their homeland. That didn't mean that the new amenities were bad, they were rather enjoyable.
"I do not see how you were not angry with me, Wangji. I would have been angry with me if our positions had been different," he tells him.