Problem with understanding two sided Matching Algorithm: maximium cardinality
The standard definition of the stable marriage problem is, given $n$ men and $n$ women, find a stable matching that marries all of the men and women.  Consequently, by definition, everyone will be matched and the number of matches will be exactly $n$ in any solution.  So, no, what you mention cannot happen, if you use that as the definition of the stable marriage problem.

I'm not 100% sure what your text is referring to when it talks about maximum cardinality matching, but I suspect it's referring to find a maximum matching in a bipartite graph, which is completely separate problem.  In this problem, the matching is not required to be a stable matching and it has nothing to do with the stable marriage problem.