The signcryption and the authenticated encryption are both the combine of encryption and authentication with three natural composition (i.e., EtS, StE, E&S). I am not sure that if they are the same cryptographic primitive.
If they are the same, why a cryptographic primitive has two different names?
If not, the only difference I personally found is that signcryption is a symmetric version and another is an asymmetric version. But I strongly believe that the difference I found is not true.