I'd imagine there was either one person who made a bunch of ships to showcase the ship building or maybe several people from the team have made ships and they just took a bunch of them at the end for the trailer. Possibly the person taking the different ships for the trailer didn't know that it was a Starsector ship. Or maybe it's an easter egg.
(This came up like a year ago; IIRC the shot shown there is from a mod for that game.)
This seems like an official kickstarter trailer. Rimworld has a spaceship mod called Save Our Ship 2 and Stardeus looks very similar to it. Someone else made an extension for that mod that adds the Hammerhead, Sunder, Aurora and Apogee as possible enemy ships. Looking it up, someone also made a Conquest in the mod. I wonder if you're thinking of that instead? The mod author also seems to know/like Starsector.
EDIT: this is also an older trailer, there is a new one now for the closed alpha which seems to have no remakes of Starsector ships.