They have the number one class right now based mainly on numbers. IF they keep this class together, they will finish with a top ten class but certainly not number one. ...
All the Class Ranking are influenced by Quantity. As IM3 notes UM will probably have a Top 10 Class.
This year's rankings should be a better guage than past years now that the SEC can't bring in a class of 30+. In past years the SEC schools (and several others) usually dropped in the rankings due to non-qualifiers, greyshirts, MLB, etc.
UM currently has a Star rating of 3.61. We can debate Stars but I've found them a more relative guage of the respective teams and classes. Last year ND's average Star rating was 3.61 and ND finished 7th on NSD. Currently UM is that same 3.61 while ND is up this year to 3.77.
If you look back through the years you'll see that Southern Cal was ranking up 4.0 classes year after year while ND was in the low 3. Southern Cal at 3.78 and ND at 3.77 are essentially a wash. The dominant edge in overall talent is gone. (And as is the coaching edge.)
Still lots of time until NSD. There will be considerable movement in that Top 10.