According to Gukov et al. in this 2017 paper Seiberg-Witten theory in 4d categorifies Seiberg-Witten theory in 3d. In what sense is this phrase mentioned? I know what the process of categorification is (e.g. how Khovanov homology categorifies Jones polynomial).
What is the exact relation between the 3d and 4d versions of Seiberg-Witten theory and in what sense is the latter the categorification of the former?