I'm not sure about shooting wings off- that may have indeed happened somewhere, I don't know. However, the typical WWI biplanes were similar to the Wright Bros.' flyers... had wooden frames- wings, fuselages, etc. constructed of wooden spars and ribs, with fabric stretched over them, all of it held together with struts and tensioned cables.The idea was to maximize the lift of the wings and minimize weight, because the engines were quite heavy for their power. However, those cables, struts and the extra wing created drag, and as the plane increased in speed, that drag of course would strain the wings. If the plane got into a steep dive, there would be not only the drag but centrifugal loading on the wings as the plane got to the bottom of the dive.

In the early versions of the Nieuport fighter, the lower wing was much smaller than the upper one, and only had one spar ( the beam extending the length of the wing to make it rigid). Wings on most of these planes were also thin, as it was thought that gave them less wind resistance. That made it rather weak. This and the drag and extra loading made it possible for the lower wing to fail on the Nieuports during a dive, and as that wing was tied into everything else , the upper wing, the fuselage, by wires and struts, if that wing failed the plane failed. And failing during a dive of course did not give the pilot much chance for survival. Not being stupid, Nieuport did change the design, and the later fighters didn't have the problem of "flying out of their wings". Eventually wings were also made thicker, when it was realized that it did not really create more drag and would make them stronger. And when biplanes were replaced by monoplanes with monococque construction a small failure like a snapped tensioned cable would no longer crater the plane.

Here's The Quest for Performance , a NASA article on aircraft design history that talks about the evolution of fighter planes, etc.