That would be the author’s error. She left an opening for sophisters to do their thing. That does not, however, alter the fact that an individual human being comes into existence at the time of conception.
If conception is the entry of the sperm into the egg alone, then that is not the point where the individual human being comes into existence. It takes several biological stages for the nuclear elements of the sperm to get fully involved with the nuclear elements of the egg. This takes about 16-18 days after the sperm has entered the egg.