There is only one Koran. Your friend may be referring to the Hadith which is the sayings of Mohammed.
Mohammed started his religion by saying that the angel Gabriel came to him in a cave and gave him a message from god(sounds like mormonism). He started out peaceful but had trouble finding converts. He was running low on money and couldnt get the Jews to convert to Islam so he says god told him it would be ok to steal from the infidels. Seemed to work out for him and as time went by he found more extreme measures to be very effective, such as convert or die. Its one way to get what you want I suppose.
Where I think the split comes is in the Hadith. Some in Islam say it is from god and others not so much.
All Islamic teaching eventually leads to extremism. The only way you are assured of salvation in Islam is to become a martyr for Allah.
King James Version (KJV)
Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them.
For they that are such serve not our Lord Jesus Christ, but their own belly; and by good words and fair speeches deceive the hearts of the simple.