There is nothing preventing it, although I don't know one would tell. The symptoms of MC are ususally severe and would not meet Rome criteria.
I don't know what that means unless one had IBS-C (whatever that really is) and MC since MC ususally results in severe diarrhea.
I think MC is usually treated like IBD...
From what I can tell, sometimes celiac and MC appear to be one and the same and other times not. But this statistic sounds made up and it is probably meaningless anyway: 70% of what population? Who has been tested? Many celiacs go undiagnosed and MC is probably a rare disease. Anyway, there is a related condition collagenous colitis and that makes the relationships more complicated.