He flew a special F-5 recon aircraft.
Technically you're correct; the F-5 is a reconnaissance version of the P-35 with cameras in the nose, instead of guns.
From the description of the wreckage field a few possibilities come to mind: hypoxia; loss of control, possibly due to spatial disorientation; a dive to the point of compressibility, which was a problem with the P-38 airframe, are all possible.
Funny, I knew him as the author of Wind, Sand and Stars which I first read at about age 12 in a Reader's Digest Best Loved Books for Young Readers edition. Parents should seek those books out in used bookstores; they're a well-chosen and brilliantly-edited set of anthologies.
I knew The Little Prince but never connected it to Saint-Ex! And to the writer of this piece, it was his most significant achievement!
Ah, there was a time when the French were men! It's worth remembering that they suffered three terrible wars on their own soil in the span of a lifetime. It is a truism that war has a dysgenic effect, for those that are sacrificed are invariably the nation's best men.
Au revoir, Antoine de Saint-Exupèry.
How wan the face, O traveller, this wan
Gray landscape looked upon;
And how forlornly in the high tree-tops
Lamented thy drowned hopes!
-------- Verlaine
d.o.l. Criminal Number 18F