He probably gained the CEO's trust at some point. Something like "I bet I can break into your personal bank account given public info?"

CEO interest is piqued. Gives him a business card, let's talk soon.

The on the call,

KM: what is your checking account number?

CEO: that's private

KM: it's printed on every personal check you write, so definitely not private

CEO: ok, good point, #######

KM: great, now tell me the numbers on the card I gave you

CEO: your phone number?

KM: yes

CEO: ok, ########

KM: ok I think I have what I need

CEO: really? that's it?

KM: yep, let me get to work, we'll talk soon