There is nothing special about that size of a jet engine. Ones that size have been around for at least 65 years. And we are all well aware of scalability.
You're missing that this particular engine is used for testing design concepts, not for powering aircraft.
And we are all well aware of scalability.
And that is the whole point of using this small-scale TEST engine to develop engine design concepts that can be scaled up to airliner size engines.