this is true..
there are significant differences between the jog dial and touch only (to be expected) looking at the back, the jog dial has extra connectors the touch only doesn't have and the main ones appear to even be a different shape.
but apples to apple the 2015 --> 2018 "should" be the same. the difference as I understand it is the mainboard in the unit, difference piece of hardware taking different firmware (windows CE based unit in 2015-2017 and Linux/Android Based in 2018+) .
all things being equal, if all the connectors are the same, the only real difference might be the mainboard and firmware, then there is no reason it shouldn't work.
my concern would be things like the backup sensors, camera, etc. if the other modules on the BUS need something in that old HU that they can't find they may not work, don't really know if Hyundai changed the programming to accommodate the newer HU and different OS.