Samuel ran to Eli because he heard a voice calling his name and did not realize that it was the Lord speaking to him.1 Seeing as Eli was the closest person to him, and likely also needed help due to his old age, it was natural for Samuel to think that Eli was the one calling him.
5 and ran to Eli and said, “Here I am, for you called me.” But he said, “I did not call; lie down again.” So he went and lay down.