Chinese source:
http://news.cnwest.com/content/2017-05/02/content_14808957.htm
During their 3 year relationship, he has burrowed 1.25 million RMB (around 180k USD) from her family. Initially, he asked for 400k, then another 850k later to "buy a car". He didn't buy any car. When confronted about the money, he claimed he had spent it all. She did write an IOU note when lending him the money.
Why can this be considered fraud? (the reason he got arrested)
Apparently they didn't register for a marriage certificate, so legally they are not married even had the wedding went through. Since they aren't married and there's an IOU, their relationship can be considered as one between a lender and burrower.