They are physical or they aren't physical?
Well if they come from a different existence they may or may not be what we consider physical beings. It really depends on how their existence works and the physics behind their universe.
Ill try to simplify my thought process a little bit.
Imagine a race of aliens so advanced that we can't even comprehend their thought process.
Imagine they have the ability to engineer a universe, the properties of the universe and the matter in the universe.
They create models about the design and then create the universe to study and see what it produces.
Think of 10 different universes on a pedestal side by side in glass spheres. The beings overlook all of these universes. They've all been designed with different percentages of elements and different physics. Each universe is created to be studied to see the results of that matter and those physics and ultimately what it produces biologically.
They look at sphere 1 and they observe how life has developed across the universe under those specific properties.
Sphere 2 has their physics altered and is different from sphere 1. There is a different composition of elements and a different universe is created with different types of beings and technology based on that universe.
Sphere 3 is different from one and two, etc.
All different, all contain elements in different concentrations, or maybe just different elements, possibly with different physics, all to be studied for the better understanding of biology and evolution under different systems.
We are just infact one of the many byproducts of how our universe was designed. It is designed for life to evolve and we are just one of many. We ourselves are not special, we are just part of the larger study of biological processes under different physics and we get to experience life because of it.