The description of Thomas in paragraphs 6 and 7 of the story suggests that-- Thomas has vague memories and lost his identity.

Thomas is confident and self-assured.

Thomas has been separated from his friends.

Thomas has been poisoned.

6 He didn't understand how this could be possible. His mind functioned without flaw, trying to calculate his surroundings and predicament. Knowledge flooded his thoughts, facts and images, memories and details of the world and how it works. He pictured snow on trees, running down a leaf-strewn road, eating a hamburger, the moon casting a pale glow on a grassy meadow, swimming in a lake, a busy city square with hundreds of people bustling about their business.

7 And yet he didn't know where he came from, or how he'd gotten inside the dark lift, or who his parents were. He didn't even know his last name. Images of people flashed across his mind, but there was no recognition, their faces replaced with haunted smears of color. He couldn't think of one person he knew, or recall a single conversation.