It is an inconsistency in wording, but I always understood it to mean that wall cover doesn't apply for mortars and artillery. This is reinforced by the Terrain Chart which clearly indicates that the cover of walls and hedges are NA against mortars and artillery.
But it might be a good idea for Chad to have consistent phrasing for both sections if there is another version of the rules. But I suspect v1.1 was the version sent to GMT for their eventual reprint of CC:E
I understand it that way too, it was just to mention the error for future correction.