Yup like he said...

Closing the throttle down, also reduces the aperture that permits the fuel to siphon back.

That means it runs back from the carb at a much slower rate giving you time to get the engine started.

You also don't really want to start a plane at higher throttle...

A high idle will do if you are unsure of the engine, and then at mid to low idle once you have the engine fully tuned up.