Under normal circumstances, if the spatial portal appeared not far from where Dong Tianyu was located, Dong Tianyu would certainly notice the spatial fluctuation the moment the portal was formed.
But this time, it was not until the spatial portal had formed and the intense fluctuations disturbed him that he realized a spatial portal was being created.
After ruling out the possibility that someone was deliberately hiding it, the only explanation left was that the portal was too far from Dong Tianyu's location, so he failed to detect it when it first appeared.
Actually, for those at the Magic Capital Base, portals connecting to Otherworlds occurring sporadically was no longer alarming; after all, the responsibility of clearing the Otherworldly Creatures had been handed down to civilian teams, reflecting the Officials' attitude towards this matter.