<<probably an umbrella disorder for many conditions that cause inflammation in the intestines>>
Yes and no. Crohn's is (supposedly) a very specific disorder: it is inflammation that causes damage down through multiple layers of the intestinal wall (even all the way through it). It can cause permanent damage to the intestines. (Although, it must be remembered that not every flare of Crohn's will cause very severe damage or deep inflammation--that's why it can be confused with UC.)
However, there is also Ulcerative Colitis which can contain everything from very mild inflammation to inflammation that causes repairable damage to the topmost layer of the intestines. If damage goes deeper than that, you have Crohn's.
As best I remember, both disease are auto-immune and have very similar properties. It's really just a matter of degree. Also, Crohn's can affect other systems (kidneys being one), but I don't think UC is as bad about doing that.
So Crohn's really isn't an umbrella diagnosis for intestinal inflammation--UC is. Question is, without evidence of damage to your intestines, but bloodwork evidence of inflammation or auto-immune disorder, why did they say you have Crohn's instead of UC? UC never or almost never causes permanent damage to your intestines the way Crohn's does, so it's a less severe diagnosis. The symtoms of it, compared to Crohn's, are also usually less severe. It is entirely possible that you are correct in suspecting that they were just slapping a label on you; Crohn's isn't an umbrella disease that covers all types of inflammation, but it looks like your doctors were (very wrongly) applying it that way.
Also, food allergies and even non-allergy food intolerances can cause irritation (which almost certainly looks the same as inflammation) in the intestines. However, it's my understanding that neither cause the sorts of results you got with your blood work (although Celiac's might, as it is also an auto-immune disorder which can cause visible intestinal irritation). So you are also right that doctors can miss something more simple like that and lump it under an IBD.
Have you tried cutting out certain food groups to see if this helps any? A few lucky people have been able to narrow all of their problems down to an allergy or intolerance to gluten or dairy.