I'd say if it's rubbery it probably is. If it was dark blackish brown I guess it could have been impacted stuff from your intestines. The impacted stuff sinks though, or at least that has been my experience in the past. I had a few light brown "stones" which would break (used a q tip, I'm not so brave) and were like wax in the middle. My dark blackish green ones were much a much more dense wax, almost candle hard. And I had a few which wouldn't break open at all.
Just for amusement I'll also say that I passed some grape seeds which freaked me out because they looked like cooked chicken liver and had weird slimy stuff attached. I thought I was seeing part of my liver with a parasite attached. When I finally realised that I had grapes as my second food that day I had to laugh at myself. Strawberry seeds and grapefruit pulp also look a bit freaky if they aren't digested completly:)
All in all whether it comes from the intestines or the liver aren't you glad it's not in you anymore?