Tesla is a master of framing. The miles driving without Autopilot includes situations where you can't use Autopilot anyway. The fair comparison would be times when Autopilot could be used but isn't vs Autopilot being used.

Ya, my immediate thought upon reading that was, you could rewrite that sentence to say: "There were fewer accidents while the autopilot did the easy stuff than when humans were doing all the difficult stuff."

We don't actually know if it's more safe since most of those 4.19 million miles will be driven by people paying somewhat attention while being driven by the autopilot. Not by the type of person reading a newspaper in the back while the autopilot is doing its thing.