What?!
I'm from England. I've never been to Mexico, no family members have ever been to Mexico, no friends have ever been to Mexico - I don't even speak Spanish!!
The closest I've ever been to Mexico geographically is Florida! I think the doctor is either crazy or a charlatan!
I don't know what the statistics are on the distribution of Crohn's disease throughout the world, but I'd bet they're higher in modern, industrialised Western Countries than elsewhere. I think if they ever discover what the cause of Crohn's disease is - it'll be an array of different environmental factors. It'll be something in what we eat, the additives and pollution we ingest, or even the illnesses we have (or don't have anymore), that'll point to why our bodies decide to play fast and loose (literally) with our digestive tract.