As this wingsuiter deployed his main canopy... nothing happened! Realizing that he was experiencing a high-speed malfunction, the jumper followed his emergency procedures: cutaway and pulled his reserve. However, somehow, his pilot chute managed to get caught in the deploying reserve, the lines from his main snagged on his Cookie G3 side plate, and the d-bag with this main canopy ended up dangling between his legs for the duration of the canopy flight until landing. This jumper decided to refrain from unstowing his brakes because he was comfortable landing on his rear risers, and feared that the surge created by unstowing his brakes — or any big movement — might result in his main canopy finally deploying and causing further complications. Fortunately, he was able to land safely on his rears.
This jumper admitted that this was only his second time using that particular main canopy in his container and that "its not technically recommended by the manufacturer since its too bulky." So, in other words, this jumper knew that the manufacturer did not recommend using that size canopy in that size container, and decided to jump something that wasn't appropriate.
One other possibility is that the jumper didn't give his pilot chute a good strong pitch and left it in the larger than normal burble created behind a wingsuit. When this happens, the pilot chute can just spin around in that burble and never actually leave the wingsuiter's back. This would potentially account for why his pilot chute actually ended up getting caught in his reserve as it deployed. The pilot chute may have been caught up in the burble, with the d-bag stuck in his container, and as the reserve deployed the pilot chute may have been yanked up with the reserve.
The folks who make skydiving gear know what they're doing. They do it for a living, they are meticulous in the design and testing process, and they take their jobs seriously because our lives depend on them only putting out products that are capable of saving lives when jumpers decide to participate in an activity which, by its basic nature, is dangerous. When they say that a piece of equipment isn't designed to work with another piece of equipment, it's NOT because they are trying to make you downsize more often and spend more money — it's because they don't want anyone dying while using their equipment! These aren't arbitrary recommendations, these are intended as life-saving instructions which you ignore at your own risk. This jumper knowingly ignored manufacturer recommendations and was very lucky to have walked away from this incident.
We're pretty sure that as this jumper lands... he says, "Dude, this is not my reserve!" There are two equally scary propositions that may arise from that statement. Either the jumper didn't know what reserve he had in his container or his rigger put the wrong reserve in when he was repacking the container. The former seems to be far more likely but either way, that comment is a big red flag that something was wrong here!