I am an Asian. I went into a restaurant. There were full of empty tables. I tried to seat in one of these table. Then the madame of the restaurant came to me and asked whether I would be having a lunch. I explained I was having a coffee. Then the madame told me to move to the back seat of restaurants without proper tables and chairs. Is it a discrimination?
Is it discrimination? Yes, because discrimination is a broad term that covers any situation where someone might reserve something under specific criteria.
In this case, it sounds like the restaurant reserves tables for people who will be eating. If you'e only having coffee, they only allow you in a certain section. Unless you live in some city with a very strange law that prevents discrimination based on what you plan to order, there is nothing illegal about doing that. Discriminating based on your order is not a protected class by the federal government.
If you're trying to claim that you were discriminated against based on race, you have to actually prove that happened somehow. Based on your summary of the situation, it doesn't sound like that is what happened. Simply being of another race does not automatically qualify it as racial discrimination. As an example, finding proof might involve asking or looking around to see if "tables are for people ordering food only" is an established restaurant policy that applies to everyone. If there's a sign up somewhere, then it's clear they were just following a policy.