Scrum Masters are true leaders - please elaborate

It means that they realize they are in the service of others. They do not subscribe to the conceit that others ought to serve them. They understand that true leadership is exemplary and inspires others to higher greatness.

The most critical distinction being that a Scrum Master will actually do it.

Thanks for the explanation @Ian

What is the current understanding by Scrum community the scrum master stances? I think it a little bit evolved for years. Going from 10 stances then to 8, 6 stances in PSMII training etc. 

Is manager and leader both SM stances? Or maybe this is different dimension? Does scrum master manage scrum process or lead it?

I ask from formal perspective (PSM2/3 questions that touches the topic)

I think it a little bit evolved for years. Going from 10 stances then to 8, 6 stances in PSMII training etc. 

Stances are the elements of a Scrum Master's social vocabulary. You need enough of a vocabulary to navigate human challenges with fluidity.

Is manager and leader both SM stances? Or maybe this is different dimension? 

A vocabulary like this is emergent, and the elements you learn to use are selected according to context. It might be appropriate to leverage 10 stances or 6 or 8 or dozens of them.

Does scrum master manage scrum process or lead it?

You manage what people have in their heads about Scrum, and what it means, and thereby lead its successful implementation.

thank you!