People do accidentally report their wages incorrectly. I expect the UC Division is well aware of this but there is also a sizeable group of people who actively engage in unemployment fraud, i.e. purposefully underreport their wages or continue/open UC claims while they're fully employed. When the UC division initially sees a discrepancy, they can't tell the difference between an honest error and someone engaging in fraud.
Mainly what the UC Division cares about is getting the money back. My caution was just so that you don't continue to make accidents when reporting your wages. If there is a pattern of that, the UC Division could conclude it's fraud and not just an honest mistake.

