What he means by damage prevention model is tailoring your kill order and CCs in such a way to minimize the damage done to the group, especially the tank, thereby increasing group survivability, etc.
And as for the rest and how it all works, elites do more damage than strongs, it's just that the ratio or mob damage to mob HPs make it the smart move generally to kill weakest to strongest. I don't remember the numbers but I think it's something like a strong mob does 25% less damage than an elite, but the elite has twice as many HPs. So just to use some completely made up numbers to illustrate the point...
Say you have 1 strong and 1 elite in the group, takes 10 seconds to kill the strong and 20 to kill the elite, 30 seconds total fight time no matter what order. Elite does 400 dps, so at 25% less the stong will do 300 dps.
If you kill the elite first that's 400 dps for 20 seconds - 8000 damage taken, then the strong dies so that's another 300 dps for 30 seconds - 9000 damage taken for a total of 17000 damage in 30 seconds.
Conversely if you kill the strong first that's 300 dps for 10 second - 3000 dps, then the elite dies so that's another 400 dps for 30 seconds - 12000 damage taken for a total of 15000 damage in 30 seconds.
So by killing the strong first you prevent 2000 damage from being taken by the tank. And that in a nutshell is the damage prevention model. CC the strongest when possible and kill the weak first to minimize incoming damage and reduce the likelihood of deaths and wipes.
Sounds legit and makes way more sense then the guy saying to CC strongs over elites