I realize that I'm replying eight years after your last inquiry, but I, also have relatives on the 1873 Concordia, and in one manifest they are listed on the same page as your Carl Johnson.
My 2nd great-grandparents, Julius Bernhard Carlsen Lund & his wife, Johanna, plus their infant daughter Hulda somehow got out of that mess in Moisie. The Molsons were making obscene amounts of money at the time, and yes, they are the same Molsons who own the brewery. They also owned a railroad, a lot of forestry land, and a bank that printed its own currency. I wouldn't put slavery past them.
I have found a copy of a New York Times article that claims in June of 1873, 215 Scandinavians pirated a schooner from Moisie, and sailed up the St. Lawrence Seaway to Point Levi, where they were captured. The story made national news and was paraphrased and re-printed in over a dozen other newspapers I have found.
Julius & Johanna somehow made it to Chicago from there, then to Collingwood and Parry Sound Ontario, finally settling in Cheboygan, Michigan in 1881.
I have been searching for almost a year for any other news about this incident, and have just about given up. Perhaps court records or newspaper archives from Levis or Quebec City might give us a clue as to how this was resolved? The time in question is late-June, 1873.
Contact me and I'll open up my tree for you, there you can see the NYT article.