This is correct. There is no stated methodology that explains the calculation of the "development rating". I can only say this, the "development rating" appears to increase if you have more recruits. So if one school had 20 Top 247 recruits, and 10 were drafted, but another school had 40 Top 247 recruits and 20 were drafted, the second school would have a higher "development rating".
Thus, even though Miami has a HIGHER percentage of Top 247 players drafted, we are aced out by the fact that UiF signed more Top 247 recruits. Which, of course, seems silly on its face when there is no clear way to understand the mathematical calculation.