Having lived in MIA for too long, I can tell you that the airport and its operations are more becoming of a banana republic deep in the African Bush than for the USA.
Other than the daily corruption that occurs, drug smuggling by airline employees as well as criminals with a long sheet working for baggage services, you also have employees who play basketball with packages and small suitcases (as caught on tape by a local TV crew). So the fact that your bags showed up and are not riffled through and your valuables stolen, should make you very happy...
But yes, the explainaintion is crap, but he really can;t tell you that the guys did not feel like working hard that day, can he?
I know it is not what you had in mind, but 45 mins is really good for MIA.
Next time, by pass MIA if you can...