That's cope, they said specifically that he would be able to as long as they have a regular humanoid physique (so not the centaurs)
tbf VC did churn out a lot of children later when viliage fertility got boost by fairy queen.
but my take is that every race already got low fertility in the first place
Dragon: despite live for more than 1000 year Des only have about 5-6 child(i forgot)
Elf: male have low sexual drive/ strength + long live race have low fertility
Oni: same as elf
Bonus: vampire , it impossible for them to get pregnant in the first place with ancestor also confuse about it. but he just didn't care.
that and Hikaru only have 1 night for almost every women in village.
if we also look at life-span of each race he impregnate. i think the speed we got is already a lot for one man.