The advantage, or disadvantage, of having a Classical education is one knows Latin, Greek and several other languages. It was great when I worked in Athens since after a week or so the words started to flow. So what is the gripe?
First the Latin word for wall is murus. Thus a wall painting is a mural. You see, mur in both. Simple.
Second, the Latin word for street is via. Via Appina, the Appian Way.
Now what do you call a street painting.? It is NOT a mural, that would mean it is on the wall, not if it is on the street. Could it be a Vial? Closest I can get.
But each time I hear them say mural I get sonic dissonance. It is not a wall guys. It is a street. But it really says more of our culture and its failings than anything else.