something.
I knew it! I emailed a different RD after another marathon where a 3:14 marathoner did a 18:30 split for 5km (flat course, no hills) and they said "within the scope of possibility, we won't DQ". This 18:30 (6:05 pace for a 7:15 pace marathoner? yeah right!?) split was on the out and back section. They also missed a mat at a key turnaround (obvious they cut).
The RD said "we won't DQ without further evidence". Basically, it doesn't matter what the splits say. RDs won't DQ anyone unless it is more than obvious.
This is a case in point. RD probably thought within the realm of possibility that he missed all the photogs.
Even if they had mats and you skipped every one, they'd probably do nothing!
The BQ standard is a joke. You need to beat it by 5% in order to beat the cheaters.