In Simple Words
Bitcoin is open-source software. That means its code can be studied, copied, and used to create another similar system.
But Bitcoin is more than just its code.
It is also the real network used by people, miners, nodes, and services around the world.
That network has grown over time and cannot simply be recreated by copying the software.
So another project can copy Bitcoin’s code, but that does not automatically make it the same network.