Sherlock took stock of John. Horrible quarantine sweats; didn't bother to change, few days beard stubble; no girlfriend, dark stains between his first two fingers...

"You've been...smoking."

He really believed that Sherlock jumped to his death. But how could that be true.

"It never happened, John. Clearly."

Clearly. Though he knew that this place was no respecter of time or continuity. John could very well be from a time where Sherlock had done just what he said.