I don't think you should eat that.
As previously mentioned, people with IBD should not have to defend their dietary needs and each person may have different diet requirements. Some people with IBD may not be able to handle fruits, but vegetables may not bother them at all. In the same token, just because gluten or spicy foods may cause flare ups in some people with Crohn’s disease, there is no single one-size-fits-all diet that all people with IBD must strictly follow.
Trust them and let them make their own drink and food selections.