It wasn't a straight-line journey from Olympus to Hell, as there were several universes between them, and travelling through them took time.
Within that time, Hades didn't know what was happening in Olympus, but the drifters, who had an inter-universal network of information, certainly did.
Arthur had come to meet Hades and Cattleya immediately after meeting Larry, the head of those drifters in this region of the Multiverse, and he hadn't hidden that fact from his parents.
"The confidence in your voice when you mentioned Zeus possibly not being in Olympus was strange," Hades said, pointing out the distinction he'd noticed in Arthur's tone earlier when he spoke.
The man noticed this discrepancy because Arthur was speaking with certainty disguised as probability.
