It appears that both planes (the one in shot and the one the shot is taken by) are mid-bomb. The former has at least two (or probably three, though the lowest could be a ground feature without checking the undigitised stock) visible bombs in a string that's probably got more on the way. The latter has four bombs, at least, from just released down to potentially the earlier one(s) in the whisp of cloud (though I think everything is higher above them than would allow for that).
Hard to tell what bomb-size they are, but typically the B-17 would carry 4x1000lb or 8/9x500lb bombs (or even more smaller ones, or a mix). I was initially inclined to believe the "bomb verification" photo has been triggered as the last of four of the heavier ones is dropped, for 'pre-impact' assessment of what was being dropped and where, but in checking I was right about the plane-type I came across
this photo which is almost certainly the same incident and suggests more bombs and a 'shutter click' per release... edit: no, wait, I got fooled by the photo-flip, it's the exact same shot, and its subtext actually says 1000lbers, now I bother to read the extra info... so I thought I was wrong, but I was wrong, I was right!Anyway, without following up the references, my best guess is that the "combat box" formation that the 'flying hedgehogs' used to merge their various arcs of defensive fire on any Luftwaffe attacks, involved a slightly staggered and offset multi-layer set of 'wings', and in the heat of reaching the mission target one or more plane from one or other 'levels' of the box has gone a little too fast/slow and/or adjusted the heading a little (perhaps at the behest of bomb-aimers striving for the exact same ground-feature in their Norden bomb-sight) or even a 'same wing' plane doing this while not noticing a few dozen feet vertical drift up and/or down from the mission plan and concentrating on avoiding wingtip clashes.
Given the quantity of bombs dropped by the number of simultaneous planes sent over so many missions, I'd be surprised if this sort of thing didn't happen a few times more (plus basic direct mid-air contact to various degrees of damage, at times of evasion if not during the supposedly steady bomb-aim/drop phase), with or without recoverable photographic evidence/testimony.
(Leaving this here under the "Reporter" remit, as I think my small amount of confirmatory research counts for that, even if it obviously aint Ukraine/fast-jet/current-day/etc, and no doubt a more thorough analysis on this same incident has been done by countless others across the nine whole or partial decades in which it was possible to do so.)