I don't do a lot of parachuting, generally, but this is not really how you're supposed to do it.

Reddit user CBalls, who posted the video, explains:

This guy is the Jumpmaster on this plane (ie. The guy who looks for the drop zone and determines when everybody should jump). While looking for the DZ it appears the rip cord on his reserve parachute gets caught on something on the ramp and deploys. He's still got his main chute attached to the plane though, so he's now got two parachutes opening at the same time. [...] I assume he just rode it in. The reserve should have been fully opened by the time the main chute opened, so entanglement shouldn't have been an issue. But, I've heard landing with two parachutes open is not a pleasant experience.

Yes, let's assume he just rode it in, and not something way worse. Here's the full video, action around :28