No, the dude is right - if they’re moving “zero fast” upon exiting the portal, then that means they’re either a 2 dimensional paste on the surface of the portal (dead), or they were entirely transported upon contact (cannot partially enter a portal) which is explicitly not how the portals in the game work.
This is because: if your hand goes into the portal and appears on the other side, it must move out of the way to make room for your arm. Because it is moving, it has velocity, which means it has momentum. If it doesn’t move out of the way, then you’re now 2 dimensional, and dead.
Also, in portal, energy is absolutely created. Every time you portal to a higher place, you gain potential energy that you didn’t have before, without losing any of the other kinds of energy that you had.