Of course there is a genetic component.
The specific individualized version of our immune system is initially built by our genes. Experiences (including in the womb) modify the genetic blueprint a bit. Other experiences (like antibiotics, or quitting smoking) seem to permanently dysregulate the immune system in some folks (i.e., in some blueprints but not other blueprints).
Once the immune system is dysregulated, consequent changes in the mucosal epithelial cells, and associated changes in the luminal bacteria, seem to create sensitivity (antigens) to foods that did not previously exist. So food can be related to symptoms, possibly to triggering a flare, or ending one sooner.
But this is different from food causing the dysregulation in the first place. As far as what to eat after getting IBD, I posted a link and summary of a recent article on "diet and IBD".
https://www.healingwell.com/community/default.aspx?f=38&m=2328117
Two of the goals (i.e., HOW it is thought to work) of SCD are the removal of foods likely to have antigens, and the manipulation/restriction of available food for gut flora, which hopefully keeps bad flora from blooming. These ideas are consistent with findings about what all is going on within IBD.
I think when you start talking blood-type diet, you are very far removed form whats going on with IBD and any logical explanation for HOW it helps. I also think that statements like "we cause our own inflammation" play dangerous blame games.