Hi Fraser!
Now, this is an interesting puzzle. My first guess would be rustproofing coating. Thorn are really good about treating the inside of the frame tubes with a Waxoyl-like or Wurth cavity wax to prevent rust. Assuming some might have collected in a little pocket, it could have migrated, and would smell strongly -- not unlike linseed oil.
Thorn are also good about lubricating the seatpost and shim (if used) to prevent corrosion, as well as the BB eccentric and so some might have accumulated bit by bit just below the seatpost collar with the frame inverted until enough collected to account for what you see draining out of the upside-down bike.
A bit of extra oily stuff inside the frame wouldn't cause concern unless it came from the BB, but that would be more in the form of grease, if anything, and there would be other signs of things amiss.
Hope this helps, and congratulations on your new bike; those Ravens are really something!
Best,
Dan.