You didn't set a condition for the breakpoint, so it was hit for a BlockStone instance, which uses SoundType.STONE.
Set the condition of a breakpoint by doing the following:
Show the Breakpoints view (Window > Show View > Other... > Debug > Breakpoints)
In the Breakpoints view, right click on the exception breakpoint and select Breakpoint Properties...
In the Properties window, check the Conditional checkbox
In the large textbox, enter the condition this instanceof BlockWoolSlab
Click OK in the Properties window.