Sheldon said Tam is on his enemy list for not moving to California with him when he left at age 14 to attend CalTech. However, on Young Sheldon, Tam and Sheldon stop hanging out when Sheldon graduates high school and begins attending college while still in Texas. When Tam is seen one final time in the final season of Young Sheldon (after three years of not appearing on that show), Sheldon doesn't even realize that Tam had graduated high school since the last time they spoke, proving their friendship was over long before Sheldon moved to California.
Howard is holding his fork, then not, in consecutive shots in the cafeteria as he prepares to eat his lunch.