Invitation letter from a friend but was denied

I applied for a 2 weeks tourist visa at the Chinese Embassy in Ghana and was denied...
I had a letter from my friend , a document from his university confirming student status , his resident permit , my bank statement with over $20000 .... the person who vetted my documents said i should get an invitation from home office in China .... I was surprised at his conclusion cos the website says a friend can invite you to visit China ....