That is the official blatant lie.
The real stats were around 10%, most of which blank or invalid ballets. They had to show up for election for one reason or another, such as the draftees or gov employers, so they casted null votes.
Here in Iran the only permitted source of statistics is the regime. So most every stats, like inflation rate, currency exchange rate, gdp, election...are inaccurate, even exagerated lies.