In what basis the 'students helped' counter counts?
Here's how that works.
The students helped counter works by counting the number of times people have viewed an answer that you have contributed to.
In other words, every time a student lands on an answer that you have contributed to, the count increases by
The bigger the number of views from a certain location, the bigger the dot and, of course, the higher the number of times your contributions have been seen.
You can find more info on how the contributions map works in this blog post.