Just on the IBAN itself being wrong that's unlikely, if it was it would have been rejected when presented to the bank. A single wrong digit will definitely not result in money ending up in the wrong account.
The IBAN number includes two check digits, these digits are created by doing some form of calculation of the rest of the digits in the IBAN number.
What these check digits do is validate the rest of the IBAN number.
So if you make a typo anywhere within the IBAN the IBAN will come up, when typed in to a computer, as being an error because the 2 check digits will be different from the value calculated from the rest of the digits.
It's not completely foolproof as if you type in more than one error there'd be a very small possibility of you recorrecting the check code.
These check digits used in most long typo prone identifier numbers, credit card numbers, ISBN numbers, etc..