It might actually be useful to think of that as an equivalency because “c” is the fastest rate by which one part of the universe interacts with another part. I think of the universe branching off by the further in spacetime these interactions have to travel. The whackiest QM interactions are still bounded by “c.” The distances between events are called space-like precisely because light/etc would have to travel faster than light to go from A to B.
The person(s) you're talking too are not talking about epistemology. If something happened yesterday and I am not aware of it until I read the paper today, the thing still happened yesterday. If I never read about it, the thing still happened yesterday.
Whether/when I "know" about it is separate, and not what they're talking about.
Then there’s ER=EPR to try to conceptualize.