Yes, it's pretty easy to disassemble it and find out. It's basically auto-updates, some closed-source extensions like Chromecast (although you can manually download the Chromecast bits for Chromium if you'd like), some branding differences as compile-time #defines. https://chromium.googlesource.com/chromium/src/+/master/docs...

(Do you know that all of Chromium is in fact open source? Have you looked at the source and the build process? Are there any parts in it that are actually precompiled binary blobs?)