It is true that many things contribute to why someone chooses to send food back at a restaurant, not just financial wealth. However, the fact that someone sends food back remains a strong indication of their financial status. It is true that someone from a modest background could send food back due to their knowledge and appreciation of the cuisine, but their means are still limited to the price point at which they can access the particular restaurant in the first place.
At the same time, it is possible that someone from a wealthy family could send food back due to their pickiness and assumption that they should always get what they want. If they come from a luxurious background and can afford to eat at Michelin-starred restaurants, it is safe to say that they are likely coming from a place of financial abundance.
So, while there are indeed nuances to consider when determining why someone sends food back at a restaurant, financial wealth still plays an important role. Considering the other factors, such as confidence and pickiness, does not necessarily undo Nikhil's point about the correlation between sending food back at restaurants and having money.
UrRong - though Nikhil may not have hit the nail on the head, one thing is for sure: if it's free, no one will send it back!