He is a good friend; he shows concern when I am hurt.
My personal reasoning is that "He is a good friend" is a complete sentence but he decided to continue it so the semicolon separates the two complete sentences "He shows concern when I am hurt" and combines them.
I hope this help with the question you're on and future questions like this one :)
This can be titled as either "word choice" or "diction". Both of these refer to how the author uses specific words, language, or slang to set the mood of their writing piece.
