I agree with this somewhat. Gluten intolerance from what I understand are less black/white and more a spectrum with celiac disease being at the extreme end of the syndrome
I think it is not so much a continuous spectrum (discrete maybe), but the fact that there are many possible sensitivities.
Coeliac disease is an autoimmune disease that is associated with an IgA reaction to Gliadins - there is more than one variety and so there are a few different types of Coeliac disease. Interestingly, IgA is associated with viruses - essentially the body thinks compoents of gluten are a virus! Tests include serology and endoscopy - though this merely indicates damage, rather than the cause of the damage. You must have another endoscopy after a long period of being on an elimination diet to confirm diagnosis.
But you can also have typical allergic reactions - IgE reactions. Serology, skin prick and skin patch tests are used to diagnose this.
With regards to IgG antibodies, the body creates these antibodies against everything we eat, so the existence of such antibodies is not indicative of disorder (so a lot of those off the shelf colour change type IgG 'allergy' tests aren't very useful). However, in principle very high levels
(way above normal), may be indicative of disorder.
Some people may be sensitive to Prolamins in general, which means they will be sensitive to wheat, barley, rye, corn and oats.
But there may also be other nonspecific sensitivities to wheat, potentially due to microflora interactions or 'leaky-gut' etc.
I for example get Dermatitis herpetiformis from wheat, but have not tested positive to coeliac or allergy tests (skin prick, patch test and anti gliadin serology).
To confirm you need to go on an elimination diet - the problem is that you have to be really careful about what you eat - many processed foods have wheat derived ingredients, or contain incredients processed on the same production lines as wheat derived ingredients. In Australia, food labeling is very good, but occasionally, they will not mention wheat derived products and merely say something like "natural flavours" (some manufacturers explicitly state "(contains wheat)" after specifying "natural flavours".