If you're using rectal meds, it's common for the rectum and sigmoid to look more quiescent and then active inflammation shows up again in the descending colon -- that can still be a presentation that is consistent with UC. If you're not using rectals, then this pattern would be more consistent with Crohn's.
Chronic inactive colitis usually means that the tissue isn't currently inflamed but has architectural changes associated with chronic inflammation in the past. Sort of pre-pre-pre-dysplasia.
Granulomas on biopsy would be definitively associated with CD, but looks like there were none of those.
As pb4 said, the medical management is pretty much the same. Your options fork a bit if surgery comes into play, but often the surgical options are more palatable for CD than UC (e.g. Crohn's colitis patients can have a straight resection, often without a diverting ileo; UC patients almost always remove the entire colon).
dx'ed UC pancolitis 5/12
past meds: asacol hd, VSL#3, apriso, rowasa, xifaxan, 6mp, cortifoam, pentasa, cimzia, canasa, butyrate, flagyl, cipro, prednisone, remicade, methotrexate, cholestyramine, cortenema
current meds: none!
step one: colectomy, end ileo 1/16/13
step two: j-pouch construction, loop ileo 5/1/13
step three: takedown 7/31/13