Hello @Yihyun. My apologies for the late response.
The NPC Thomas spawns in Temple Of Truth Room 11.2. The screenshot you've posted is of Temple Of Truth Room 11.1. When doing the Temple Of Truth dungeon, the room you get is randomized, so you effectively have a 50/50 chance of getting either 11.1 or 11.2. So to get Thomas, you will have to keep trying until you get the 11.2 room.
I know this may not be the answer you wanted, but that is just how it is.
Let me know if you have further questions.