I run trains on the G&O garden railroad. In direct sunlight our Atlas O gauge rail and our LGB G gauge rail gets much hotter than the ambient temperature. In many cases the rail becomes too hot to touch. The same thing happens to brass and diecast engines running in direct sunlight.
I suspect that real rail also absorbs energy in direct sunlight and may be much hotter than the ambient temperature. I am sure that the investigation will look at the rail's actual temperature in addition to the ambient temperature.
I look forward to reading the investigation report. NH Joe