I saw this tweet when it first came out this morning...
The dashcam footage appears to have been from a truck just behind the accident as it happened - the footage has been slowed down so it's hard to tell how fast all vehicles involved where traveling as the incident unfolded.
I've been listening to the scanner all day long as the response unfolded. As of 5pm they are still working to empty or otherwise safe the tanker which was leaking thousands of gallons of gasoline from the time it turned over. I suspect the highway will be closed all night in one or perhaps both directions as they work to cleanup the spilled gas.
Let's all be careful out there - you never know when something unexpected will unfold around you.