“on the rock.” This “rock” became an altar (Judg. 13:20).
“and he did a wonderful thing.” The “he” is ambiguous, and that ambiguity is in the Hebrew text. The Hebrew verb is masculine singular, but it could refer to Yahweh or the angel, who was acting as Yahweh’s messenger and agent. It is likely that we are meant to understand that the angel did wondrously, but was acting under Yahweh’s direction and wielding Yahweh’s power, and thus the native Hebrew reader would simply understand that the "he" was the angel as the agent and Yahweh as the one directing the angel. It is hard to make the English clear when the Hebrew is not clear without making the English say something that the Hebrew text does not say. For example, if we replace the “he” with “the angel,” as some versions do, we miss that the text likely includes Yahweh along with the angel.