The second sentence of their response makes the first sentence a lie, they do, as anyone who grew up in our culture does, know what a Christmas bonus is, they said it to be sarcastic but also yo position themselves as a kind of stoic, who’d had a tougher life than the person asking the question.
It’s a step removed from “You were Lucky! We had to work 24 hours per day for a sixpence with no days off and 48 hours on Christmas day”