This refers to airlines that have Hand baggage only fares and do not grant a free bag for *G members on these fares, e. g. Lufthansa Group. (Heck, even if you have *G in LH's own program you don't get a free bag).

As LH Group is one of the heavyweights in *A, the rule was "adjusted", to allow them to introduce this concept. (They don't sell the Hand baggage only fare when you purchase an itinerary involving two LH Group carriers).

This has nothing to do with A3's own flights. Like before, as a *G you can bring a bag for free on A3 flights even if you purchase a GoLight (Hand Baggage only) fare.