Filter Cascade: Additions and Multiplications per input sample
Their numbers work out right if you do the stated decimation before the stage, and you pay attention to the fact that decimations are cumulative.
So stage one operates at 1/3 of the input rate, stage two operates at 1/6, stage three operates at 1/12, and stage four operates at 1/48.  If you scale the adds and multiplies by those numbers, then their stated numbers work.