I can say up front that it was not chyme; chyme is a vivid green color, made so by stomach acid, not brown.
I once read, whilst getting a digestive issue of my own corrected, that it is, in fact, possible for a human to vomit fecal matter, but not under normal circumstances. It is a sign of a clogged-up intestinal tract, which is something that definitely merits a visit to the doctor. Anyone who's had bad constipation episodes knows what I'm talking about.
If it's been happening frequently, or you've been having sickness on and off for longer than a week, it's probably not a stomach bug.