In this experiment, they didn’t even bother measuring which slit each photon passes through. The 3D glasses don’t measure or observe the photons, they merely polarize them (although they do block 50% of light). The detector D_S doesn’t measure which-path information either. The researchers could have placed a circular polarizer in front of D_S, and when they get a hit they could have said with confidence “this photon came through the top slit!” but they didn’t even bother doing it this time. The fact that the 3D glasses alter the light in a manner which makes the which-path information theoretically measurable (even if not actually measured), alone is sufficient to destroy the interference pattern.