That’s where it seems to deviate a tad from what he says in the interview: his recollection of the death of his friend occurred on the same sortie as he was made POW.
But a bit of digging shows him as observer with 4 Sqn in late 1914, then with 15 Sqn, again as observer in 1916.
Intriguing. I’ll look him up next time I’m at Kew.