It doesn’t really tease a race at all. The Silent People are mentioned in three paragraphs in the rulebook for Beastgrave. They’re described as having lived in the Beastgrave many, many years ago, and as “somehow insectile in nature”, but not as bug-people. If the art on the rulebook is anything to go by, they look 99% human except with yellow eyes.
there is a suggestion that something still lives there, there’s a few sentences about how people still feel they’re being watched or hearing clicking sounds in the Beastgrave, but the Silent People are exclusively described here as people in the past tense.
I suppose you could also interpret the Ur-Grub cards as a hint, but there’s no lore or anything to do with it
They’re basically in the same position as the Katrophanes are in the Shadespire and Nightvault rulebooks - a long-gone people that inhabited one specific city/mountain, used to fill in the lore of that season of Underworld’s setting. Seeing as the Katrophanes were never released as models, there’s no reason to suspect we’ll get the Silent People either.
EDIT: It’s possible we could see something for them in the next season of Underworlds which looks like it’s going deeper into the Beastgrave setting, but I still believe a full faction release, at least any time in the near future, is extremely unlikely