They’re not looking at the phase relationship between the two pulses. They’re looking at the light’s frequency. Moving one of the diamonds would introduce a phase shift, but that wouldn’t explain the frequency shift.
But even a single diamond, all by itself, can absorb and release energy via photons. The explanation for this is conventional and isn’t being tested here. I’m just wondering if the supposed entanglement is just an artifact of the synchronized wave front and nothing spooky.