It is quite simple, I think that David Cameron has unintentionally misled parliament.
In Prime Ministers Questions on the 4th of November, David Cameron on being asked about the NHS winter crisis mentioned that the Royal College of Emergency Medicine was in favour of the Junior Doctors contract. (Click the link above or wait until 8 minutes and 40 seconds have passed.)
Unfortunately, based on information in the public domain, this is not the case.
Royal College of Emergency Medicine does not appear to be in favour of the contract.
It will be interesting to see if Jeremy Corbyn takes him up on this next week!