Algodoo

Not to be picky, but technically your scene is not a "Rube Goldberg" machine. It is simply a series of actions that trigger other actions in a sequence (such as a series of Dominoes falling down). Many other Algodoo users have gotten it wrong too. So, don't feel bad!

A Rube Goldberg machine is one that takes a normally simple and easy task (such as eating a slice of toast) and makes it very complex with a series of mechanical actions and devices that ultimately end up doing the wanted task.

See: Rube Goldberg Machine

So technically it's just a "contraption"?

Sure, you can call it that.