Which is neither here, nor there.
For one, concepts are also physical things (e.g. the correspond to chemical changes and neuron synapses in the brains on those knowing about them).
Second, even if abstract, concepts still affect the physical world by influencing actions.
Besides, nobody argued morality is a physical thing.
>It's also relative from person to person and from a culture to another. It is not a truth.
Physical things are also perceived differently rom person to person and from a culture to another. A dish might be great for one, but disgusting for another, for example.
Something being relative is opposed to it being absolute, not opposed to it being true.
E.g. if I say I love X, that is relative and personal. But my love can be true.
We actually don't know this. People have qualia, which is an unexplained physical phenomenon. It could be that the universe comes with some universal signal that twists the thought processes of all beings with qualia, so as to shape their feelings about moral questions, to align them with true universal morality.
Obviously, I just made this up, and even if it were true, maybe you'd call the signal false universal morality, but it could be a physical thing.
We did but it is a concept not a physical thing. It's also relative from person to person and from a culture to another. It is not a truth.