Nick left the inside of the Containment Unit but didn't leave it completely.
Right now, Nick was between the inner walls of the Containment Unit and the outer walls.
There was a millimeter of free space between the two walls for air to flow through, and Nick used this to move towards a specific spot.
In the past, Nick wouldn't have been able to fit through such tiny openings, but ever since he had become a Specter, his mist ability had improved a lot.
Nick could easily fit through an opening that was only a millimeter wide without using any Zephyx, and he could also cause quite some damage in his mist form.
He had been able to improve his ability by changing the manipulation lines on his Specter Core, and he was nowhere near done.
His abilities would only get better with time.
A bit later, Nick reached the place where the employee entrance of the Containment Unit should be.