Well we know there are only two memory slots and that there can be no more than 16GB in each slot for no more than 32GB total. Crucial spells out DDR4-2400 or DDR-4-2666.

ASUS most likely filled only one memory slot. We do not know what kind or size. I would suggest he run HWiNFO and try to copy what memory is in the laptop now.

Red arrow points to what slot (in this case slot 0)
Yellow arrow points to what size of memory in that slot (in this case 16GB)
Blue arrow points to what type of memory in that slot (in this case DDR4-2400 /PC4-19200 DDR4 SDRAM SO-DIMM)
Black Arrow points to what timing of the memory in that slot (in this case 17, 17, 17, 39)