Continuity mistake: When Sam is in his bedroom, after he finds the Cube sliver it falls and dramatically burns a hole through the floor into the kitchen. But Sam's bedroom is over the living room (there is nothing on the ground floor below Sam's elevated bathroom, and in the first movie Jazz hides in this open space), and the kitchen is actually located between the den and dining room, at the other end of the house. If they were to follow the actual floor plan of the house, the Cube sliver would have landed in the area of the piano in the living room, but where would the fun have been in that? (00:12:30)
Chosen answer: He knows from stories passed down to him from older generations of bots, not much unlike stories about the past passed down to us from our ancestors. His line about no one telling him anything is just a way to avoid being put back in the box or being tortured by Mikayla.
dablues7