Okay, I've figured out how although I'm not sure if this is a thorough solution.
1 Keys in Registry Editor
It seems that the registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\GameUX
is related to the Games Folder. Inside, the key with a GUID name ( on mine) contained all the custom added games. I checked which one has the steam game's name (Torchlight) and removed it.
2 Removed from AppData
I went to:
C:\Users\IvoryTower\AppData\Local\Microsoft\Windows\GameExplorer and removed the folders which have the same GUID as the games you deleted from registry
I found this by searching the registry for Torchlight and then searching for the same in Windows Explorer..