Where Did Quenty Get The ROBLOX Loading background?

It's a Standard ROBLOX Loading Screen. It means that the game you're trying to enter has too many people in it. It is likely a person trying to join a server with their friend in it, and ROBLOX have found the game as too many players in it.

Anyway, this is not a scripting related question so I will close it after this answer.

What you're going to want to do is right click on a ROBLOX Player or ROBLOX Studio quick links on your computer. You should see a menu of options one of them being "Open File Location". Once you click on that what you're going to want to do is find the folder named content. Open that folder and go to Textures. Once you have the Textures folder open you will find the Portable Networks Graphic (png) file of the Loading screen texture in the folder loading.

Hopefully this answered your question.