So, I'm a noob at German, but I'm trying to read a book on Nietzsche and in some part the author characterizes Nietzsche as "ein ... Sprachkünstler und Sprachartist". What is the difference between a Künstler and an Artist? How could I interpret this?
You may have tripped over the different meanings of “artist” (e.g. English) and “Artist”.
In German, the word for anyone expressing themselves through or creating art is “Künstler“ (as art = Kunst).
An Artist ist an artist using his body, e.g. an acrobat. (So Artist is a subset of Künstler.) A second meaning of Artist, especially in compound nouns, is „a master of his or her profession and tools“, figuratively doing handstands and somersaults with them.
So Nietzsche is characterized as someone who created art from and with language and was a master in using language.
Künstler := Artist, one who uses imagination to create aesthetics.
Artist := Performer, esp. in a circus; Artisan, one who is skilled at a craft.
The passage describes Nietzsche as being both able to create vivid scenes with words (the first sense, Künstler), as well as expressing those well and concisely (the second sense, Artist, like a wordsmith).