Correct. 8th-gen would be required to update the bios. You could get lucky and the Z370 was manufactured AFTER the date the bios update was released. But it's almost impossible to tell that before you buy it.
FYI, that's an entry level Z series motherboard with low end VRMs, if you're planning on overclocking (or think you may ever want to upgrade to an 8 core CPU with that mobo) you may want to invest in a better board.