Why did gally think that something was fishy about thomas in maze runner?

Gally suspected something was off about Thomas because he arrived in the Glade with no memories, which was unusual compared to previous Gladers. Additionally, Thomas exhibited behaviors that challenged the established order, such as his determination to explore the Maze despite the dangers. Gally, who valued the status quo and safety, viewed Thomas's actions as a potential threat to their survival and the stability of their community.