How can the Hanbury Brown and Twiss effect (photon bunching) be explained if photons don't interact in free space?

To explain it with the influence of the two photons on the two detectors simultaneously would seem strange to me, because of the fact that "if the source consists of a single atom which can only emit one photon at a time, simultaneous detection in two closely spaced detectors is clearly impossible" (same Wiki under the "Quantum interpretation" heading).

Comment: The question is not about uniting or dividing two photons, which is possible only on the atomic level. The question is about synchronizing two photons from different sources like the sun.