No, the optimizer is not retrieving anything, it just assumes that there are 2400 rows because that is the number of rows that exists in the statictics for this table. The optimizer just tries to find the best plan and to optimize the query plan for execution taking into consideration all information that can be found for this table (it also looks in the statistics information about rows from this table).
So, whats it assuming here as rows(2400). Could you explain this.
It is assuming that there are 2400 rows in this table. Probably you've deleted some rows from the table leaving just one.