Your "vague suspicion" is absolutely right. The jacket in this article is identical to the one in the illustrations in Jouineau's book on the French Imperial Guard. Intriguing that the article mentions that the owner of the jacket, H.T. Verhoef, was an assistant surgeon and not fully qualified. The article speculates that a possible reason for the unusual brown colour might have been to conform to the brown uniformed infirmiers at the hospital.

Rod