Causation means one event actually brings about, or contributes to producing, another. It is a claim about the mechanism connecting two events, not just a description of their timing or co-occurrence — and this site’s working definition of a coincidence is specifically an event relationship where no such causal connection is currently established (see what is a coincidence?).
Establishing “no causal connection is currently established” is a statement about the present state of evidence, not a claim that no cause exists at all — see what randomness does not explain. Human perception defaults to inferring causal, often intentional, narratives from mere co-occurrence, which is exactly why this distinction needs to be made explicit rather than assumed — see agency and causal inference.