@Cyoteblack
You're confused about one thing, who did what (and yes that is very important).
Your comment would be on point.....had she been the one to give him the cup. There would be no reason for him to think she meant that romantically due entirely to what you said. However, that's not what happened. Despite the horror of repeating myself,
he was told the significance of those cups and then immediately hands one to her. Even if he doesn't think she sees him in a romantic light, it doesn't take much brains to realize that it can be seen that HE sees HER in a romantic light from his actions.
It's quite similar to buying a ring, being told by the clerk that it's an engagement ring and then just giving it to the female friend who came with you as a gift. It invites a misunderstanding, and one even the smallest amount of brain power could avoid. Simply give her a gift more fitting a business relationship.