It's not so much the glass as it is the coatings that are applied to it. Clear glass only reflects about 4% of the light that hits it, but there is a lot of sciency stuff behind it. Obviously, an entire highrise of glass is going to reflect more that a house window, it's simply math. There have been instances of large buildings with coated glass actually melting the siding of adjacent houses.
If this sound wall had a gloss surface, and therefore highly reflective, it could impact neighbouring buildings and cause problems for motorists, particularly at low sun angles.