I can't be sure if the author of Soul of Searing Steel is serious because I can't directly understand the author's writing style and attitude.
The author's writing attitude is usually influenced by many factors, such as personal writing style, writing purpose, writing experience, and so on. Some novelists would spend a lot of time and energy to conceive the plot, shape the characters, and construct a worldview to create an excellent work. Some novelists might pay more attention to the entertainment and drama of the novel and ignore the seriousness of the writing.
Therefore, it was impossible to determine whether the author of Soul of Searing Steel was serious or not because it depended on the author's specific situation and writing style.
The answer is: "OST song" refers to the song in the OST. OST referred to the original music in movies, TV series, and other film and television works, and the song part was the OST song. According to the search results, some OSTs of movies and television works included some songs, such as the theme song of the TV series OST of " A Thought of Passing Mountains," many of Zhou Shen's OST songs, and Yu Kewei's Top Ten Classic OSTs. Therefore, an OST song referred to the song part of the original music in a film or television work.