They are. You really have to go out of your way to instantiate UObjects without them getting cleaned up during world teardown. (See: RF_RootSet, AddToRoot, etc.) And if you do end up with a lingering object in the end, the engine will throw all sorts of warnings at you.
What you’re seeing is simply the internal counter incrementing with each instance. This counter allows object names to be unique without having to manually name each one of them.
In other words, don’t worry about it.