The fiction has no temporality. A game mechanic which linearly affects a non-causative, 'past' in the fiction can function as a ret-con whenever you need it to.None of that describes a chance encounter which is what the advocate of that system described it as doing. Now if he's mistaken that's fine, but my objection is having such a mechanic produce chance encounters.
The system isn't a chance encounter, it's a literal changing of the preexisting fiction.
But, in this case, it doesn't matter, the fiction has no temporality, and, therefore, no causatives, we just see it that way.