hang on to that UK bank account for as long as possible. Once gone, you won't get one back.
I doubt that they were interrogating you - just updating records; Nat West did it recently.
I doubt that the bank staff would know the difference between residency, domicile and certainly not tax status. Remember, you receive any income in the UK it is taxable - therefore you always likely to be "tax resident".
Paint your own picture of your life and hold that picture for when you get questioned like........I am a UK resident but I am in a position where I am spending a fair amount of time in Asia.... etc, etc