Port raid authors are randomly chosen members of the Writing.com community, mostly yellow or blue cases. I try to pick authors who are usually 'under-the-radar' (older members of the community) who you are not aware of. Spotlight authors are mostly newbies (black cases) and it's a way to get Angel members aware of these new writers and to encourage them with your reviews/comments/visit to their portfolios.
Does that answer your questions?