You definitely deserve congratulations for not removing the bowl you found. I'm impressed with your adherence to the rules.
The bowl may be much more recent than you suggest, at least based on my understanding from our local "indigenous" culture. I don't think the technology for making bowls emerged until later, although I'd have to verify this from my notes. Our "indigenous" cultures did have a healthy trade with the mainland, transporting the steatite bowls they carved to the mainland in tomols. It is reported that these tipped in the surf spilling their payload... and there has been a rise in sea level post-glacial that may have inundated sites.
Again, very impressive that you left it where it was!
Dr. Bill