An latimes article says NHTSA says they were going to investigate regardless, that it wasn't at Tesla's request. I rather suspected that was a bit of spin from Tesla. Still good to get it done though regardless.
Feds investigate Tesla fires: Elon Musk's idea? NHTSA disputes that - latimes.com
Feds investigate Tesla fires: Elon Musk's idea? NHTSA disputes that - latimes.com