Capsule collider and Rigidbody not sinking?

Unity Engine
1

I load the project “AngryBots”. There is the main hero “Player”. He has Capsule collider and Rigidbody (use gravity), but the floor DOES NOT have Mesh collider. Despite that fact, “Player” does not sunk through the floor.
How?

2

I have added to the “Player” a new script and it shown me, that there are simple colliders in the “Colliders” group object. So there is separate collider on the floor.