I've never been asked if it's my first audax. Whereas for QG and a heap of the women in my club, being approached under the assumption that they're plausibly less experienced than the (male) approacher, in every cycling context we go to as a club, is the norm.
As an example one of my club friends has podium'd at Grinduro in Scotland. At the cross race season this year she repeatedly had men telling her how important it was that she go tubeless, why hydraulic brakes are the best, etc. Where for you being asked 'is this your first audax' is a one off, being approached and perceived and assumed as the less experienced and incapable is understandably wearying and irritating.
Even when I can tell someone is new to the sport, knowing being assumed that this is the case is very, very annoying and it's best not to ask IMO.