That phone call was set up to protect his family. Despite everything that has gone on, he is taking the blame to protect his family. Even the threat is set-up to protect them from the Nazi's. More than ever, Walt is a provider.
In the fire station, there is a chess board with a White King moving out of the corner, protected by a single pawn. Walter is the White King, and he's about to make his final moves.
Also fun trivia, whilst he's pushing the barrel, he passes his pair of pants that he lost in the first ever episode
