Those two things don’t square. If you’re moving relative to the mirror when your fire the photon, it would hit in a different place than if you were stationary. The photon can’t be moving infinitely fast in your reference frame for that to happen.
Yeah I think infinite is the wrong word for them to use there. Maybe call it maximally fast? Like it goes as fast as possible no matter your reference frame, but that speed is limited by the speed of causality. The photon has 100% of its skill points in speed through space and 0% on speed through time.
Would it? What does “stationary” mean when discussing relative velocities? The mirror being stationary and the person firing the photon moving at a constant velocity is literally an indistinguishable scenario from a stationary person firing the photon at a moving mirror.
If I am moving relative to a mirror when I fire the photon, then the mirror is moving relative to me, and will be in a different relative position by the time the “event” of my firing that photon reaches it.
Also, the photon isn’t moving infinitely fast in my (the firer’s) reference frame. It’s moving infinitely fast in it’s own reference frame.
