I mean, I’ve worked in agriculture pulling weeds in those temps and setting up irrigation lines. It was literally 30° F hotter in my job where I stand in front of the kitchen door a couple weeks ago. It’s a far cry from comfortable, especially if you don’t have access to water, but I can’t imagine dying from it, absent some other health condition that was aggravated by it.
Also, just to be clear, I absolutely think it’s abusive to leave an inmate in such conditions without access to water and shade, I’d just be surprised to hear it was fatal in an otherwise healthy young person.