Well yes, but I assume they started by saying "Is that Samarrange?" and I said "yes". Now it's true, I could have been someone who had nicked my phone and was impersonating me, but it doesn't seem like a very likely thing to do. And in the unlikely event that someone had targeted me for phone theft and was waiting for the bank to call so they can discover my current account balance (bwahahahaha), they would probably have nicked some other details too.
Again, at some point, someone has to trust that the other is who they say they are, and I don't trust people who call me, but I mostly trust people whom I choose to call. But there's always a level of risk. If it's just my current account balance leaking out to a random phone thief, meh.
There was a scam in the UK a few years ago where the scammers were pretending to be the bank's security department. They called people on their landlines and said "Of course, we know there are lots of scams about, so we want you to hang up and call us back at the number on the back of your card, so you know it's us". But what the victim didn't know was that (at least at the time), a call to a UK landline is not terminated until the caller hangs up. So the victim hung up, lifted the receiver and heard a dial tone (which was being played to them by the scammers), dialled the actual number for the NatLloyds security department, then heard the phone ring two or three times (again, a recording) and was answered, "Hallo, NatLloyds security team... Mr Smith? Oh, thanks for calling us back, yes, we just need your debit card and PIN number, we'll send a car round to collect it".