Jinx... Was literally reading the same page right now. This has been derived from a report by stratfor.
The 18 trillion yuan is including loans from Local government financing vehicle( LCFV)
which are loaned out of local body coffers.
CRC, as a corporation, is not liable to repayment of these loans.
These are expected to be paid by the local, provincial govt. since they enjoy the added economy benefits that high speed rail produces from the beginning as manufacturing, employment spur and long term benefits like real estate value enhancements and growing mobility of working class.
On a construction scale basis, its a bit easier to understand. CRC produces a km of hsr at $25-30 million(2018 numbers, aggregated average over tunneling and viaduct construction), over 30,000 km the cost can be $750-900 billion (6 trn yuan). So its quite unlikely that total loans have crossed this figure since debt has been routinely serviced. Also, i don't think the hsr program is entirely credit based, with central government taking up at least 20% of annual financing of hsr from revenue reciepts directly.