Entering personal info might also be understandable. My employer gives a Christmas gift. This year they asked us to update a form with our temporary address if we were in a different location.
But a cash bonus? That's the epitome of something that 1) should go through payroll and 2) should just get direct-deposited into your bank account as is the case with your regular paycheck. There's no reason why you'd need to provide any additional info.