There's more to it than that.
PZEV vehicles, whether hybrid or not, also must release ZERO evaporative emissions. They must have some sort of sealed intake system so they don't release any fumes while parked. And while running they are so clean that in smoggy areas, the tailpipe exhaust is cleaner than the air that the engine breathes in. They also have a variety of advanced pre-catalysts and engine controls so they are very clean on cold startup, which is when most cars produce a big chunk of their emissions.
Now, the Insight may win something back because of its better mpg -- i.e., under some conditions it may have lesser emissions per mile.
But overall, I'm afraid that a new Prius beats the Insight soundly on emissions, especially when you consider its all-electric mode at low speeds.