In what way is language arbitrary?

The truck driver backed his vehicle between two buildings, he did not have an inch to spare on either side. fragment, run on, or complete sentence?

The greatest gift the sumerians gave the world was the invention of writing. the sumerians were wealthy people. they needed some way to keep track of what they owned. they began drawing pictures. they used a reed as a pen. they drew on soft pieces of clay. the soft clay was then dried in the sun. the tablet became a permanent record. later, the sumerian drawings changed into wedge-shaped symbols. this kind of writing is called cuneiform. by putting symbols together, the sumerians could write entire sentences.

When you see information in brackets, these are dialogue stage directions setting actor names