Weird behaviors of SQL

I have a question about this exercise. When you use COUNT(*) with GROUP BY, the system seems to automatically know that you are counting the numbers in each category, not the total number. What if I group by some fields that are never repeated in the table? Will this force the system to count all entries?

https://www.codecademy.com/paths/analyze-data-with-sql/tracks/analyze-data-sql-calculate-and-summarize-data/modules/dspath-sql-aggregates/lessons/codeflix/exercises/count2