Metal toxicity wouldn't only manifest itself in the intestine, you would have a wide range of symptoms that aren't present in crohn's disease.
What has been suggested is that tiny pieces of metal, called microparticles, would end up penetrating the intestine, get stuck there, and cause non-stop inflammation.
Your body would also develop an allergic reaction to those types of metal after a while. They tested all this in studies.
It's another theory of crohn's disease, that people inhale or ingest tiny microparticles, they get stuck in deeper layers of the intestine and cause inflammation.
It's also suggested because for whatever reason, crohn's disease rises the more developed a nation becomes, with industrialisation comes inhalation and ingestion of microparticles.
It's been suggested in relationship with EN too, EN is extremely low in microparticles. Food you buy from a store isn't "clean", EN on the other hand is quite a lot cleaner, it's abscent of most types of microparticles, because of the way it's made, packaged and used.