You are no longer breaking the brick yourself, merely smacking it against another object. This same theory applies to holding up two bricks with a space between them or standing two blocks together with a slight space so that you can strike one, causing them to slam together and break on impact. If you do not explain the difference of the method to the audience, it is fraud. While patio blocks are fairly stable, red bricks and some other blocks will weaken if left in the sun. Baking bricks has the same effect and is completely fraudulent.
Bricks can also vary greatly in hardness due to the manufacturing process.
Bricks bought from a yard from the same pile can vary due to sand content as well as exposure to the elements. Generally, lighter colored bricks are easier to break.