Discuss the credibility of Boo's defense of Jem and Scout?

The credibility (believability) of Boo coming to help the children is accurate. It seems he has been keeping track of the children from inside his house—putting items in the tree, laughing at their games, fixing Jem’s pants, giving them a blanket during the Miss Maudie’s fire. Since Jem yelled “loud enough to wake the dead,” it would have alerted Boo that the children needed help.