Could mean any number of things, such as a lot of Banks prefer to have parental addresses, rather than Student digs addresses, due to the temporary nature of residence in student disg, there one year, gone somewhere else the next in many cases. Or that Smile have a problem with their computer systems. Or that Smile's Credit Reference Agency has a problem with it's computer systems.
I don't have a Smile Bank Account, but other people that I have heard with ordinary Smile Bank Accounts have seemed pretty pleased with the service they have had from Smile, so I think you will not be kept waiting too long.
It could be that Smile and it's Credit Reference Agency have no previous Credit records for your 6 year old house, if no-one at that address has ever applied for a Bank Account or Credit from that address previously.
I know individuals only build up a Credit Reference when they do take out Bank Accounts and/or take Credit or Borrow, when individual details are then entered onto a Credit Reference, as super good, good, indifferent or bad generally.
Individuals are of course always linked to one or more addresses. So I would guess if there had been a succession of bad debtors at a particular address, the address itself would have built up something of a reputation, or if good Credit references had always applied from an address, the opposite would apply presumably.
So it is possible that as it is possibly your first Bank Account, you do not have any Credit Reference by which the Agency can judge you, say to advise the Bank whether to give you a Current Account, and possibly an overdraft or not and for how much etc., or whether to advise that they can only provide you with a Savings Account. That is an Account where you can deposit and save money and make withdrawals, but only from and up to your Savings Credit Balance.
All of these things are risks when a Bank decides to give a new Applicant a Current Bank Account and whether to issue merely a CashCard, or a Debit/Cheque Guarantee Card, as to whether a new Applicant is likely to get into debt and default or be a good Bank customer, earning lots of money for the Bank, or rather indifferent neither lending nor borrowing and paying off any credit cards on the due date, so never incurring interest.