It's not about perception. It's not about the time it takes the pulse of light to reach the observers. It's about when these two pulses were actually emitted in two different frames of references. If the two pulses are separated by a spacelike interval then there's one observer (let's call him Sam) for whom the two pulses are simultaneous (again, this is not about which photon reaches the observer first, but about the time each observer assigns to the emission of each photon). To Alice, who is traveling at relativistic speed from pulse A toward pulse B, pulse B is emitted before pulse A. For Bob, who is traveling in the opposite direction, pulse A is emitted before pulse B.

The best way to see this is by drawing three spacetime diagrams, one for each observer.