The writer of that article seems to be somewhat confused. He/she is describing the S73 as a sedan and an SUV in the same paragraph (!)
There are two new platforms: S2-E (S2 Expansion) and S3. The sedan codenamed S73 is about the size of an Aion S and utilizes the S2-E platform. The SUV which appears to be a product on the S3 platform is codenamed S59 (and not S31) that has already been confirmed by a supplier which is providing seats for both the vehicles.