Why is the SAL75300 called a macro lens?
It has 1:4 magnification, I thought only 1:1 lens are considered macro?
It is primarily marketing. However, a macro lens does not need to be 1:1. In fact, 1:2 was quite common for a macro not too long ago. But, many lenses, in the past and now, are labeled as "macro" simply by virtue of being able to do 1:4 or larger magnification. In fact, a macro could also go beyond life size.
Another key ingredient in macro lens design is targeting a flat focal plane. Non-macro lenses tend to have some curvature to the focal plane. I doubt though that these lenses marketed as macro lenses acquire a flat focal plane in their "macro zone" either.