Even without the bank giving the check writer the privilege of overdrafting, either the bank or the check recipient has to absorb the loss if they accept a check for which the check writer has insufficient funds (unless the bank goes after the check writer). By contrast, with a debit card, the credit risk is much less (since the bank knows before the transaction whether sufficient funds are available).
That doesn't make a checking account (especially one without check writing) a "credit product" though, no?
If anything, anybody accepting a check for payment and delivering goods/services before it clears is extending credit in a way, but that has less to do with the bank account and more with pre- vs. post-payment for goods/services.
