The title says they found a lost island, but what they really mean is, they found archeological remains under the ground of an already known island, right?
Yes and no. They believe the peninsula where they may have found the city of Kane used to be a separate island. They think there used to be a channel that filled in over time, converting the island into a peninsula.
Almost. It's now connected to the mainland as part of a peninsula, which seems to have complicated things somewhat.