aplunk that answer really doesnt hold any weight. currently there is no definitive answer as to why sheds happen. the "hair shock' thing is a simply a theory, is the theory that the old hair is pushed out by the new. appealing though they sound, none have to my knowledge been backed up by research.
as to spironolactone not causing shedding, there are many people out there who would agree with that, and an equal amount who would disagree. i've heard of many instances when spironolactone apparently caused shedding, all anecdotal though.
spironolactone as a topical treatment is a far less invasive treatment than propecia, and is commonly thought to have no systemic effects. that could be your answer right there.