How can an algorithm have exponential space complexity but polynomial time complexity?

Question

For enumerating the minimal feedback vertex sets of a graph Schwikowski and Speckenmeyer show an algorithm "GENERATE-MFVS" in their publication "On enumerating all minimal solutions of feedback problems". It is said that it runs in polynomial time but uses exponential space in a dictionary.

insert F_q into Q and into D;
while Q is not empty do
  remove any set F from Q;
  output F;
  for each uG-successor F′ of F do
    if F′ is not contained in D
      insert F′ into D and Q;
    fi
  od
od

How can this be? Does an exponential number of insert operations to the dictionary not inevitably imply exponential time?