It's called "thumb break" or "thumb over bore" where the user utilizes a hand-stop, foregrip, or any other conspicuously protruding part of the fore-end as a contact point that is pulled inward toward the body while the thumb is placed on top of the fore-end, or over the bore, for increased stabilization.
I wouldn't say it's a comfortable way to carry a rifle, but for a good number of people, it feels better to do this while shooting. What's so good about this method is not only the integration of the practice of using an angled foregrip or hand-stop and the close-quarters/carrying utility of a vertical foregrip but also the benefit of easy shooting by essentially pointing your entire arm in the direction of aim. It seems to be getting pretty popular.
I was going to comment on it (though my sarcasm meter is through the roof since ezekill is generally around whenever there's a gun post), but the weird thing is the positioning of her thumb. Everyone I've seen doing it or depicted doing it keep their thumb parallel to the barrel instead of monkey-gripping it. My experience isn't anywhere near exhaustive, though.
I was going to comment on it (though my sarcasm meter is through the roof since ezekill is generally around whenever there's a gun post), but the weird thing is the positioning of her thumb. Everyone I've seen doing it or depicted doing it keep their thumb parallel to the barrel instead of monkey-gripping it. My experience isn't anywhere near exhaustive, though.
It would be much more instinctive to keep the thumb parallel with the barrel ergo "pointing" at your target, but this instance may just be simple oversight. I've seen it done both ways though, so it might also be personal preference.
Personal preference and situational cases. Some people feel they have more purchase when they bring their thumb over the top. I tend to bring my thumb over the bore whenever I'm using longer handguards with or without handstops. Foregrips, my thumb is pointed forward. It's similar to how you'd grip a pistol with your control hand. Sometimes there are handguards that are shaped in such a way that I can't really bring my thumb over the bore comfortably.
It would be much more instinctive to keep the thumb parallel with the barrel ergo "pointing" at your target, but this instance may just be simple oversight. I've seen it done both ways though, so it might also be personal preference.
From my own personal experience of training others (I do it free, so I am not a professional; take this with a grain of salt), I find that there really isn't any "instinctual" grip. When people first start to shoot, their hand positions and grips are wildly different from another new shooter. In personal training, the thumb over the handguard vs parallel makes zero difference in my performance. With a stock AK-47, I can't get my thumb over without obstructing iron sights (unless I use my zahal rail, which has separate, higher, iron sights). Also, on my AR-15 and AK-47, I have a push pad switch module that made which is mounted to the top of the handguard just above my AFG. I put my thumb over the bore so I can manipulate that module which controls my light, laser, and red dot (visible/ir).