First the IRS will debit or deposit to any account you list on the return it is banking policy to not allow persons not on the account to use the account and usually block deposits for non account holders ... this is up to the individual bank's rules.
Now just a guess ... $1400 is the exact amount of the stimulus credit so was that on the return incorrectly ? If he got the advance he does not also get the credit. Did the IRS deposit all of the expected refund then recall only $1400 of it ? Did they see the pending deposit and spend it like it was posted (not good judgement ever) ? Then find out all of the anticipated deposit was not allowed which caused the overdraft ? Until the pending deposit is actually posted the IRS can make a change to the amount to be deposited or withdraw the deposit altogether.
Check with the bank to see what happened and with the IRS to see what they actually did.
