There is approximately 2% of IBD patients that have both UC and CD so it's quite rare....because CD can affect any part of the GI tract, there are different terms to describe the 5 common areas (5 subtypes of CD)
The five types of Crohn's disease with their symptoms are:
Ileocolitis: Ileocolitis is the most common type of Crohn's disease. It affects the small intestine, known as the ileum, and the colon. People who have ileocolitis experience considerable weight loss, diarrhea, and cramping or pain in the middle or lower right part of the abdomen.
Ileitis: This type of Crohn's disease affects the ileum. Symptoms are the same as those for ileocolitis. In addition, fistulas, or inflammatory abscesses, may form in the lower right section of the abdomen.
Gastroduodenal Crohn's disease: This form of Crohn's disease involves the stomach and duodenum, which is the first part of the small intestine. People with this type of Crohn's disease suffer nausea, weight loss, and loss of appetite. In addition, if the narrow segments of bowel are obstructed, they experience vomiting.
Jejunoileitis: This form of the disease affects the jejunum, which is the upper half of the small intestine. It causes areas of inflammation. Symptoms include cramps after meals, the formation of fistulas, diarrhea, and abdominal pain that can become intense.
Crohn's (granulomatous) colitis: This form of Crohn's disease involves only the colon. Symptoms include skin lesions, joint pains, diarrhea, rectal bleeding, and the formation of ulcers, fistulas, and abscesses around the anus.
There can be overlap between these types of Crohn's disease. Some people have more than one area of the digestive tract affected.
You'll notice the last one (crohn's colitis), this may very well be what your doctor is referring to...often they confuse patients when they don't elaborate on the terms they're using when discussing with the patient.
With CD, it can affect more than one area at the same time as well. UC is limited to the colon/rectum.