Case not closed. If you are not the biological parent, the kid is not yours.
Then I guess he's a kidnapper, or else what's he doing with the kid.
Why don't you tell millions of adopted children that their Moms and Dads aren't really their Moms and Dads.
Your view is consistent with a purely animalistic or biological view of the world.
But, if this is your way, why does a child ever have to be any man's? The women gestate and give birth. No reason for the man to be there or have any responsibility in this view.
So, go all the way with it why don't you.