They are definitely distant, but she is not uncaring. Even though he thinks she does not know where he is going on all of his quests for the "Blacks" in New York, she is quite aware and even calls ahead to let people know he's coming and to look after him. All the Blacks are caring, although a little odd, since they are all suffering after the 911 attack on the Twin Towers. In this way, his mother is actually mothering him, albeit secretly. She and Oskar are bonding in their suffering and loss of the husband/father in the family, but they do it in a different, less obvious way than most would expect.