Looked at the photos. This certainly could be worm castings; it looks almost like what I excavated Monday. I had to insert a trowel and take scrapes off of the sidewall of my excavation until I worked my way out to recognizable compost again.
That stuff was like clay.
Since your worms have had much longer to work, it's likely that what you have there is worm castings as well.
Wow. You might have to take some OUT of the SFG...