It can make you feel good and feeling good improves healing. Petting a dog or cat will do the exact same thing. If a rock makes you feel good, the effects of that rock are the same as a joint.
I seriously doubt this. It's more likely that the extract used, cannabiol, has properties that stimulate bone growth and strength, and that this has nothing to do with pscyho active properties.
It's worth reading the study though to see the experimental protocol. Was the amount of food eaten controlled, set the same between the group given the extract and the control group?
If the effect of the extract was simply to stimulate eating, that could explain the experimental results. Maybe rats with broken bones don't exactly feel like eating, and rats with broken bones given the extract want to do nothing other than munch on doritos in sheer blisss....