It becomes evident as the relationship between Anne and Peter develops that Anne is much more confident and talkative and that Peter is very shy and quiet in her presence. Note, for example, the following quote:
I managed to get hold of Peter this afternoon and we talked for at least three quarters of an hour. Peter had the greatest difficulty in saying anything about himself; it took a long time to draw him out. He told me how often his parents quarrel over politics, cigarettes, and all kinds of things. He was very shy.
Perhaps we are able to infer from such descriptions that Peter is naturally somebody who lacks in self-confidence and is somewhat overpowered by Anne and her natural confidence and talkative nature. Anne is clearly more intelligent than Peter and is able to think more deeply and critically about things, and perhaps this is why Peter responds in the way that he does. This is of course the central reason why Anne ends the relationship between them, as she didn't feel that Peter was her intellectual equal.
As Anne gets to know Peter better and wants him to care for her, she spends time with him in his attic room. In February of 1944, she notes that she and Peter share many similarities. They both have mothers who don't understand them, and they are thoughtful about their emotions. However, Anne's tendency is to create noisiness and be energetic, while Peter withdraws into silence and solitude.
There are many comparisons that can be made to the differences between Peter and Anne. One comparison is that people handle misfortune and misery either by withdrawing into solitude and hiding or by making connections and being talkative. The other comparison that comes to mind is the way in which some Jews at the time decided to fight the Nazis in armed uprisings, such as in the Warsaw Ghetto Uprising of 1943 (which could be likened to Anne's turn to noisiness and boisterousness), while others tried to resist by hiding or other means (which could be likened to Peter's turn to seclusion). Neither means of resistance was right or wrong; they were just different ways people tried to survive the Nazi onslaught.