Maybe not directly, but it does have an impact. According to this, it's got to do with accidental gluten ingestion and a lack of intestinal healing.

https://celiac.org/study-shows-slightly-increased-mortality-in-celiac-disease/

From the end of the article, emphasis mine:

"The great majority of people with celiac disease live long, healthy lives. And yet, the fact that we’re still seeing the signal, even in the most modern era, says that despite the improvement of awareness, increased diagnosis rates and easier access to gluten-free options, there is still a measurable impact on the ultimate outcome, which is mortality in people with celiac disease."

Maybe there's a co-morbidity thing going on, but either way my point is he knows there's a real problem because he's been hospitalized as a result of eating wheat, so he takes no more chances.

Yeah I unfortunately have celiac along with many people in my family and have never heard of it causing an immediately life threatening reaction. Pain, embarrassment, mental issues, long term mortality, a whole slew of problems but not "I'm going to immediately die".