While the file size has changed, there is no visible loss of quality. Radiant Photo saves an optimized file, and the enhanced pixels can occupy less disk space.
The dimensions of your file have not changed. You have the same resolution. This means the image will display and print at the same size.
If you want to take more control over what is exported, please see this page.
https://manual.radiantimaginglabs.com/1/en/topic/choosing-file-settings
Note: Some DNG files on Windows OS may not follow this rule due to a bug in the Microsoft components we rely on for reading RAW files. At this time, Windows hands off the embedded preview instead of decoding these files, resulting in an image with 1/8–1/10 the original resolution. Our development team is actively seeking a solution. We hope for your understanding in the meantime!
As a workaround, you can increase the DNG preview resolution when creating your DNGs.