The database is user database and now it is under System Databases in SS management studio.
Let me explain how it moved under system databases-
1. Third party tool was used to configure replication.
2. By mistake the name of the user database was entered at the time of specifying the name of distributor database. (SQL server ent. manager does not allow you to enter name of user database as distributor db but this third-party application allowed).
3. Third-party tool changed the is_distributor value to 1 for the user database in sys.databases.
4. Replication configuration stopped in between as the same database was being used as publisher and distributor
5. is_distributor value was not changed back to 0. It's value is still 1.
SSMS shows databases named master, model, msdb or tempdb, and any other db where the field is_distributor = 1 in the view sys.databases in System Databases container.
Now, the challenge is to change the value of is_distributor to 0 of the user database.
exec sp_helpdistributor does not return anything. It says "Command(s) completed successfully."