Why doesn't a photo reflecting off a mirror collapse it's wave function?

photon*

I've recently read about the Elitzur-Vaidman experiment and was wondering why the reflection off the mirror doesn't collapse the wave function (not the beam splitter, the normal mirrors) And why can't you measure the impulse of the photon hitting the mirror to see which path it takes, if the absorption and re-emission of the photon by the mirror (if that's even how that works) doesn't collapse anything. Maybe my basic understanding is wrong or maybe just a nuance, but I can't quite wrap my head around it.