Male child taking his mothers last name

I am researching a friendfs Japanese family.
I identified her grandfather, born 1871 in Fukuoka-ken, Japan, who immigrated to Hawaii and the grandfatherfs sister.
I hadnft been able to identify her grandfatherfs parents until I found the grandfatherfs sisterfs Hawaiian marriage certificate listing her parents.
It appears the grandfather took his mothersf last name.
Is this a common practice?
Thanks,
Bill

It is not common practice anywhere in the world.

Do you mean that you have proof that the parents were always lawfully married under the father's last name, but the child took the mother's maiden name even though he was never adopted? In other words, are you saying that the child had a last name different from both his parents'? If so, that's quite uncommon.

Meanwhile, it's quite common for the whole family, including the father, to take the mother's last name. It's also common for a child to be lawfully adopted by a relative on his mother's side, so that the heritage won't die. It's also common for an unmarried woman to have a child between a man.