"Oh...I was just thinking that I would like to treat you," there's nothing strange about that at all...except for the fact that Sylphiel isn't all that certain what the currency would be in this world.
If it's a date or a friendly outing Sylphiel doesn't make the distinction, anything that would make Zelgadis feel better in this case, "I know you like tea...but...I don't think I've ever asked you what you like to eat?"