Maybe a better way to put it would be "Graph Neural Networks are a Generalization of Transformers". The formulation of "X are Y" indeed suggests that you could

Maybe a better way to put it would be "Graph Neural Networks are a Generalization of Transformers". The formulation of "X are Y" indeed suggests that you could just have stuck with Y instead of using the special case X, whereas in reality they took Y and added something to make it more general.