Wouldn't that intern just use an NLE (be it Premiere, Davinci Resole etc) anyway? If you need to style subtitles and edit shorts and video content, you'll need a proper editor anyway.
He does use davinci resolve but only for 2.
NLEs make ffmpeg a standalone yet easy to use tool.
Not denying that major heavy lifting is done by the NLE. We go a step ahead and make it embeddable in a larger workflow.