It is.
Not sure about this. As you know, at this time of the year, their official answer will be “you’re not tax resident in Taiwan”. (I don’t know how far they take the logic of this argument though, i.e., if they insist because the foreigner isn’t tax resident here they must be tax resident in their home country instead.)
That should be how it works, yes. I don’t know specifically about HSBC (maybe someone else does), but for many Taiwanese banks that’s usually not how it works in practice. There’s a whole thread about that, but maybe HSBC is better.