Which one is your blood type?

Based on WebMD it seems type O & B are both told to avoid plants which are common irritants (like grains and beans)
https://www.webmd.com/diet/a-z/blood-type-diet

I agree with avoiding those things. I would recommend everyone do so, though, not just people with type O or B blood.

As to how likely it is to be a coincidence: those two types roughly match my conception of a healthy human diet while type A and AB don't. So about 50/50. More generally, the odds of a coincidence are about 1 in 4 (assuming there's no correlation at all between blood type and optimal diet and remaining agnostic about what constitutes optimal diet).