Usually, banks share their customer list internally with Investment/loan/cc department (as thementalist said) to the point that they know approx how much amount we hold in our acc in order to push us to do investments and FDs (Investment RMs in ICICI are headache)
same people when switch to other banks take the list with them and keep using the same list... I have received calls regarding my CC which I didn't even accept (courier return)
SBI is generally an easy bait as many people hold their cards... you just keep looping them by asking "arre bhai kaunse card ki baat kare ho, mere paas toh 3 hai sbi ke"
If they are official, they would know the ending digits, if they are fraud, they will just say "visa waala" (that's what happened with you)