Not sure if it's an error, but it's a bit vague as to whether a fighter is pinned when taking a hit from the exhausts of a Gas Promethium Engine. Body Spikes specifies "This attack does not pin them" and Wheel Scythes specifies "if they are a fighter they are Pinned", but there's no mention of pinning in the description of Gas Promethium Engine. It functions more like Wheel Scythes, but I don't know if that means it should pin (because Wheel Scythes do) or shouldn't (because the book feels the need to clarify that Wheel Scythes do, as though it's an exception).
I guess RAW it doesn't pin (until I saw the description of Body Spikes I was confident that was the right interpretation).