Maybe they're making an allowance for thermal expansion...(naughty)You have a 2018 CX-5 and you've already changed the gear lub from your front transfer case? This's the first time people here are reporting the gear oil in front transfer case is low!
Everyone who checked his/her rear differential gear oil from factory and all says it way low from the fill-hole! It requires ~0.75 quarts to fill up during the change but the manual says 0.48 quarts! This's for gen-1 CX-5 AWD, the manual says the capacity on rear differential oil for gen-2 CX-5 AWD is 0.37 quarts! It'd be interesting how much it really need. Please report back your findings.
For engine oil change, if you drain the oil long enough without using Fumoto valve, it would need 5.3 quarts of fresh oil to make the oil level at "Full" mark of the dipstick.