Would it be called statistic, if it is said that there are 2000 students in the school
Yes. It's a number representing an item of information.
http://www.merriam-webster.com/dictionary/statistic
Yes, I think so. It's a number that can be used to compare or contrast with other numbers in a variety of ways.
If it's a school that has capacity for 1,500 students, but there are 2,000 students, what conclusions can you draw?
If it's a school that has capacity for 3,000 students, but there are 2,000 students, what conclusions can you draw?
What other comparisons or contrasts can you think of?
No, the information that there are 2000 students in the school is not considered a statistic. A statistic is a numerical characteristic that describes a sample or a population. In this case, 2000 is simply a count or a total number, but it does not provide any additional information about the students or their attributes.
To gather statistics about the school, you would need more specific information, such as the number of male/female students, their average age, their academic performance, or any other relevant data that can be analyzed and provide insights about the students as a whole.