Answer:
It's possible that your customer has dual citizenship with Taiwan and Canada, but your records only establish citizenship in Taiwan. As Taiwan is not on the current IRS list it appears you are not required to report the interest paid to this individual on a Form 1042S, but you could be in the future if the list is changed.
Some banks have decided to just report all NRA interest on a 1042S (assuming no 1099INT is required) and let the government sort them out.