Assalam alaikum
The person u r talking to aims to deceive you and keep telling u he is 'not convinced' when u show him how his points are ridiculous.
He said 'The testicles produce only 5% of the sperm.' So his own statement is clearly in error.
The testicles actually produce only 100% of the sperm cells.
Now back to the ayah:
" He is created from a water gushing forth
Proceeding from between the back-bone and the ribs"
To prove a scientific error, he has to 'prove' that genital organs or passages actually exist outside the area determined by God, otherwise his claims are to be ignored.
