Bert, a fuel line snagged when the prop was extended.
Fuel leaked into the engine compartment.
The extinguisher was in the car at the side of the runway.

Schleicher has since changed their fuel line material. Schempp might still be using lines that are not aviation grade. They are not aviation grade on my club's Duo XT. Don't know about others.

TW, your fuel lines likely go through the engine compartment. After a leak a retracted engine could cause a fire.
Jim