So let's have a look at what [nevr] has done to their guild channel:

As you can see by the yellow channel icon as well as the lock icon on the right side, the actual [nevr] channel is password protected.
However, all channels below are not password protected even though they where created as sub-channels of the main [nevr] channel.
The result of this is that anyone on the server will be able to enter the channels that are not password protected.
So if you want to make sure to keep folks out you do need to explicitly set the password for each channel you create.