That constitutes serious injury
Yes but it's not life threatening. The crew would have assessed the injury with the help of medical assistance, and if the injury is not life threatening, they continue. If the injured is able to physically talk, they can consent to continue. They are not unconcious, suffering from hypovolaemic shock or cardiac arrest for example which would constitiue a diversion without question.
A burn, laceration, compound fracture or even childbirth is considered serious but the persons life is not at risk, therefore there is no need to divert. Declaring a medical emergency later may have been due to the injureds condition worsening? Or declare a medical emergency to be met by a paramedic team on the tarmac?
An onboard medical kit contains almost everything to deal with all manner of injuries and medical problems. It is down to the crew and their medical support which make the decision along with the injured party and their companions.
Besides, ever hear of people breaking bones then 7 hours on a hospital trolley before being seen?
SO I suggest A330Driver, you go back to your own airline and request Aviation Medicine training to appreciate the situation before flaming other airlines. After all from relatives of those who have fallen ill onboard British Airways aircraft the crew cannot be praised enough for the way they deal with casualties. The crew are constantly tested on their medical abilities and knowledge also.