Why Andrea Iannone's 18-month ban is a complex case

Last week Aprilia MotoGP rider Andrea Iannone was handed an 18-month competition ban for an anti-doping infringement, whilst he has maintained his innocence, claiming that ingestion of the steroid came from contaminated food. Why is this case not straightforward and what does it mean for MotoGP? Lewis Duncan and Oriol Puigdemont are on the case.