remission can have more than one meaning. From the patient's point of view remission means the symptoms went away. Doctors also consider relief from symptoms to be a key goal of therapy. But GIs also have a target of achieving what is called "mucosal healing," which is basically seeing a normal, healthy-looking colon or terminal ileum when viewed through the endoscope.
A healed mucosa is often regarded as a "true" remission, and relief of symptoms is the hoped-for outcome of achieving mucosal healing. But it doesn't always work out quite that way. The appearance of the mucosa and the severity of symptoms are not always aligned. The patient could be feeling pretty good but the endoscope still shows inflammation smoldering away in the background. Or conversely, the colon could look perfectly healed but the patient is still suffering a lot of diarrhea and pain - possibly due to an overlay of Irritable Bowel Syndrome, or an intestinal bacterial infection, or Crohn's inflammation farther up in the small bowel that could not be seen via endoscopy.
So the concept of remission is not clear cut. It can be assessed in multiple ways.