It's going to get another bolt at the front bottom of the motor mount plate.
That will connect to that bottom rail of the battery rack that spans the length of the "engine compartment".
The threaded rod holds the motor well in two axis, but at the moment, the front end of the motor can "twang" side to side.
Adding that additional anchor point will prevent that from happening.
I have seen cycles where they just weld a big steel bracket to the frame. That's nice and solid, but you better make sure you get it just right the first time!
Using the threaded rod allows for side-to-side adjustment to align the motor with the rear sprocket.