The world's call didn't apply only to Noah and June. The two felt sure that every existence who opposed Heaven and Earth could hear it. The rulers had pushed the balance in their enemies' favor, forcing everything outside their control to even the situation.
Noah and June didn't question the nature of the call. They had experienced a similar power right after the life dragon's death, and they quickly confirmed that Heaven and Earth weren't faking that event to plant another trap. Noah's anger was a natural scanner that the rulers couldn't affect, and his dark matter helped in his inspection.
Truth be told, the duo would have tried to follow the call even if something ended up sounding odd. Noah and June didn't have other options, so they were willing to take risks to uncover hidden areas of the higher plane. The countdown started by Heaven and Earth forced them to prefer potential traps over safe and constant growth.