To convert a BJT into a short circuit we know that all DC voltage sources are short circuited.

Yet my professor did this:

[![enter image description here](https://i.stack.imgur.com/l7Mei.jpg)](https://i.stack.imgur.com/l7Mei.jpg)

[![enter image description here](https://i.stack.imgur.com/tZwyA.jpg)](https://i.stack.imgur.com/tZwyA.jpg)

Isn't this a contradiction? I just can't grasp the step.