I have a professional and personal interest in 737 pressurisation problems having had my own encounter several years ago. Luckily no injuries followed and to be fair the pax had little idea what the nature of the problem was, only that we were diverting.
I'm uncertain as to why 5 pax would be injured. As the rubber jungle didn't drop we know that the cabin altitude did not exceed 14,000'. The problem with the QRH drill is that if you only have a slow decompression (statistically much more likely) the a/c will overpressurise in the descent. If there is then a sudden release of pressure (overpressure valve releasing or crew manually depressurising the airframe when below 10,000') injuries could occur. Anyway, well done to the crew for getting it safely back on the ground and not thinking it was the T/O Config warning!
DM