In the Padma Purana, it mentions that Prahalad, Hiranyakashipu, Nrsingadev, they appear many times. It's not only this one time. At least 3 different...2 different incarnations in other days of Brahma are described in the Padma Purana.
One of those times he (Hiranyakashipu) worshiped Shiva and got the blessing. Another time he worshiped Brahma again. When he was worshiping Shiva and he wanted Prahalad to admit that he was supreme, then he said that, "Well, ok if you don't want to admit I'm supreme at least admit that Shiva is supreme..hes above Vishnu." Prahalad didn't accept that either.
Prahalad was very fixed up Vaisnava. He knew very clearly who the Supreme was. He got prenatal instruction. In the womb of his mother Kayadu he was instructed by Narada muni.
Narada is very merciful. So he saved Prahalad from the Devas and took her to his ashram, when she was carrying Prahalad, and then instructed her. So later she forgot a lot of the things but Prahalad remembered everything. So before he was born, he was already trained up.
The teachers of Prahalad were amazed where did he get all this information from? And they weren't teaching all this Visnu-tattva. So they were surprised!HH Jayapataka SwamiLectureNrsimha Caturdasi, 2008Sridham Mayapur