I don't really see it either there. The 'spirit' is like electricity in the links Cofty gave. They have to clarify that on death the spirit doesn't really go back to God because it becomes a way of saying 'something is alive' - which seems flatly in contradiction to the bible verses they have to address. The article addresses 'only' God raising the dead, but not whether God's involved every time a baby is made. (Because if he is, oops on the angels, women and Flood thing!).
The question is whether man making life would be problematic. And I'm not sure it is. In JW theology, God isn't involved in the production of spirit on a day-to-day basis. It's passed on, but he's the only originator. It's whether or not the means of transmission is an issue should scientists one day create life. I suspect that it won't be a huge problem for them to explain away, as the article SBF linked hints at.