Bile? Sure, whatever you like to call it. But is it "accurate" bile? You don't have to like what I post, but it's an accurate description with no feeling for either side involved unlike many others.
As for your screengrab, unless his fingers are extremely hyper-mobile at the last joint (which I will not contest, could be possible), you can see that the alignment of his his fingers are nowhere near at an angle needed to have "dug in" to her neck. Does he have a grip on her neck from behind? Yes. Dug in? Unlikely, not according to the angle of the forearm (you can see his watch) and where the hand will be located (from the fingers involved). Also, at that angle, the fingers (index and middle finger) have some of her neck and jaw covering it (not necessarily from purposely digging into the neck, although again, I won't dispute this could have been the case, only there's no irrefutable evidence), and prior to the screengrab you can see the protestor pulling her head in and raising her shoulders ala a tortoise, in an effort to prevent further efforts of restraint. This will also cause the flesh around her neck (and jaw) to raise up more easily and make it appear that fingers are digging into the neck, when they are not really.
Try and hold your own neck, it's not an accurate representation of what happened, but you'll find it is very hard to have dug your fingers in and have a good control of the neck at the same time unless you have absolutely massive and powerful hands, something I'm sure Mark Field does not have in the video, and if they did would have easily left noticable marks (and we'd have a much bigger story on our hands). The person who was being held in such a way will also have broken away their neck hold if there was any digging in easily, since it's near impossible to dig your fingers in and restrain the neck by anyone without larger hands, and the protestor had their head/neck restrained the way out according to the video.