The first few steps I would think would be similar to imine formation. So there would be protonation of the carbonyl oxygen by the pTSOH, nucleophilic attack by the amine, proton transfer to hydroxyl oxygen, then this tetrahedral intermediate would break down to via the lone pair on nitrogen "pushing down" to expel water as a leaving group.
This would form an iminium, that has the general Structure R2C=N+HR . I am thinking it is perhaps this structure they are referring to as a carbocation? This iminium intermediate has a resonance structure with a positive charge on carbon, although it is not contributing as much as the all octet N+ resonance structure.