My memory is a little Rusty, but eventually I got the joke...

If the transmission is automatic, you’re a driver.

He’s probably bump-firing to make it look like a personal hit. Benicio knows his gunfighting... he studied with Scotty Reitz at ITTS for “Way of the Gun”. So his wonky technique is likely a creative choice in the context of the scene.

Mozambique Drill.

For a much more detailed information about this story, make sure to check out the book “Arsenal of Democracy” by AJ Baime - the same author who wrote the epic “Go Like Hell” about Shelby and the GT-40. Baime’s book is fascinating and a must read, as usual.