Weeeell, his chroma (the currency of this world) is abysmal. In other words for the meal, he already has zero chroma in balance. One gains chroma through moonlacing, which means and requires holding hands or touch to generate chroma for money.

Mu has very little chroma to start with. "You don't have to. I'll pay. The meal is on me." For him, it's not really a problem, paying for a beautiful stranger.

"So take my word for it, but it's fine. Enjoy your tea and your meal. I think it's just a lovely day in this world to have a cup of tea with you, at least."