Rolf doesn't always notice a corrupted heart
EDIT: On further testing, I'm not entirely sure what leads to Rolf not noticing. In the attached save file I corrupted the stone heart in a wilderness encounter, and then immediately went to Rolf. When I give it to him and then chat he gives the normal quest rewards.
If you corrupt the stone heart while in a wilderness encounter, Rolf doesn't seem to notice and gives you the normal quest rewards instead of asking you to stop the apocalypse.