Following are the definitions of independent variable and dependent variable I found on the internet:
<1> In statistical modelling, the dependent variable is studied to see if and how much it varies as the independent variables vary.
<2> Independent Variable: variable that causes the variation.
<3> Dependent Variable: a variable whose variation is being studied.
Here in the table above, the YouTuber is interested to know what kind of people come to his "fantasy" restaurant: teens, young adults, and so on. And, kindly notice that the age groups are not meaningful, but rather arbitrary. Clearly, this isn't an experiment: I am not interested in any cause-effect. It's a survey. The Youtuber mentioned the "age group" as an independent variable and "the number of people who dined in his restaurant last week" as a dependent variable.
My question is for the same: in what way, is the number of people visited dependent on the age group? In other words, how to know which variable is dependent and which is independent in a survey like this?