Whoever wrote that just made it needlessly complex, there is absolutely no benefit from just declaring CarWashService
because they aren't making use of the additional closure that they've created. Even if they did need a closure for private state, they have the one from the outer function.
As a side note, this also looks incorrect for angular. If you really wanted a factory, this should probably be returning the constructor rather than an instance of it. This looks like it should be declared as a service.