Do chefs use customer feedback to improve dishes?
I'm only a semi-pro chef, but let's have a go at answering your question.

There are some people who have an actual impact when they provide feedback on one of my dishes. These are people I have cooked for more often and whose tastes are familiar to me. They will often function as a "test panel" when I want to try out a dish I'm considering for the menu of a commercial event I'm planning.

Should this test panel think my sauce needs more seasoning or more acidity, this would certainly cause me to adjust the recipe and/or process.

On the other hand, feedback from an individual guest whose tastes are unknown to me is pretty much meaningless. How would I be able to tell whether their likes and dislikes are anywhere near an average opinion? There those who will nearly always reach for the salt shaker when served a dish, even if to the average taste it is well seasoned.

So this hypothetical individual customer that features in your question seems pretty unlikely to cause a chef to change his recipe, unless of course the same feedback has been given before and a pattern emerges. In that case an individual customer can of course tip the scales in favor of a change.