It's a minor point ..
1. When NVMe was being designed, it was designed quite specifically to be a way of communicating with devices not raw chips, so If your definition of SSD = Solid State Device, then NVMe pretty much does need an SSD.
Of course you could do a bunch of custom work by mooching together some NAND and an FPGA or an ASIC to implement the firmware that interprets the commands coming down from NVMe and then passes that onto the a media handler to actually do actual I/O to the chips .. (with NAND thats a flash translation layer), and then put the SERDES bits in and the connector to hook it onto a PCI bus .. but at that point what you have is an SSD with an NVMe interface.
If your definition of SSD = Solid State Disk .. ie the packaging format that looks a lot like an old school SAS / SATA dieks drive, then no there is nothing in NVMe that dictates the use of that format, its just an incredibly practical way of deploying solid state devices because it works with all the existing electrical and materials handling stuff (like hot swap in a drive enclosure) most datatcenters rely on