Solid doesn't know the difference between Hard drives and SSDs, so other programs like kinfocenter always show it as a Hard drive. Linux knows the difference, see /sys/block/sdx/queue/rotational and udev's ATTR{queue/rotational}=="0"
The underlying backend, udisks, doesn't provide a method to get that info. So ideally you should file a bug with udisks. https://github.com/storaged-project/udisks/issues