I think it’s impossible to assume anything at all. With cultural, age and gender differences, it’s difficult to figure out what the intentions of another person are, unless they state them clearly. Neither you or he did that.

As a guy, I can assure you that guys do not understand subtle hints or can even logically deduce where this casual acquaintance is going from what you have already described.

You’ll need to be very clear. Maybe then he will also tell or show you his own intentions more clearly.

But first you need to know yourself what you actually want to hang out with this guy for and if it’s worthwhile maintaining the friendship for whatever reason. It makes sense if you have mutual interests or benefits from keeping in touch. However, my best guess based on your description of him offering a back massage is that he might have more romantic intentions than you. In that case it’s best for both of you to be brutally clear and end his hopes instead of “friend-zoning” him. It might feel unpleasant, but it’s crucial to be clear. If he reacts negatively, well, there’s your answer.