Use third party framework which is embedded in dynamic framework

As i understand the big change from ios dynamic framework and static is that static is linked statically to the code at link time (prior to launch) and dynamic is linked at launch/runtime

Now i have a test project:

My project have a dynamic framework linked to it - A.framework.

import A.framework

A.framework have a framework embedded inside of it - B.framework

In my main project i want to use classes from B.framework

Now i see that with a simple import statement in the main project:

import B.framework

It actually work and i can use code from inside of the B.framework which is embedded in linked A.framework

How can it be? is it something that is safe and reliable to use? How does the main project recognize the B.framework?

What about cases where the main project directly link the B.framework to the project? in this case i see many "duplicate symbol errors" at link time

Any clarifications will help