A family history of retinal detachment is one of the risk factors. The statistics show higher than normal levels of retinal detachment among Native Americans in Arizona (in one study) if that is what you mean by "Indian" ancestors. Many of them developed retinal detachment in their 20s to 40s. That is probably why they asked. Of course, retinal detachment due to trauma can occur at any age.
In addition to trauma, there are also many, many other risk factors including heavy manual labor, high blood pressure, weightlifting, severe nearsightedness, smoking (even passive smoking), and a couple of inherited diseases (Stickler syndrome and Von Hippel-Landau disease). Sometimes no discernible reason for the tear can be found.
Intraocular pressure can be a cause as well as an effect of retinal detachment. It's difficult to say what its role is without more information.
I'm glad he is seeing specialists since he is such a complicated case. Surgery is usually performed for a detached retina and most people do well. As with all surgery there is a risk of complications, but it is generally a small risk.
I don't know how much the ophthalmologists treating him have told you. so here is some general information about retinal detachment: