First you can see it originate from the base of the mountain and close the distance towards my Mavic.
Secondly, the Mavic doesn't fly that fast to "fly past something very small" and have it going that speed.
You can clearly see it come from the base of the mountain and it closes the distance between the Mavic and mountain which, is at least 300-400 yards.
First - I think the perspective may make it look like it comes from the base of the mountain but it's difficult to really tell since the perspective may be misleading.
Second - It flies by pretty fast, I'll give you that. But again, it's based on the belief that it originated at the base of that mountain which as you say is maybe 400 yards away. If you look closely though, right before it takes off, you can see a little white dot at the base of that mountain. Like the 'projectile' is sitting there waiting to take off. I think it's misleading that it "appears" to originate at the base of the mountain but in actuality it may be only 20' or so away from your mavic.
I'll admit that it looks like it's traveling as fast as a bullet, based on the thought that it originated from the base of the mountain. But I have somethings to think about.
1. If someone is at the base of that mountain about 400 yards away, how could they see your Mavic? Even with a scope it would be challenging.
2. There is no perceived bullet drop. A bullet will arch and at 400 yards, caliber dependent, it may drop as much as 5' from the origination point. Possibly more or less, again dependent on the caliber.
3. A high powered rifle round travels at 2800~3200 fps. Take a .223 for example. At that speed there is no way that 30 frames per second or 60 frames per second will catch it.
4. If we assume that the object is actually only 20' away but because of the perspective it appears much further, then a bug flying at ~10mph, that equates to ~15 feet per second. That fly by is about a second..
5. My previous comment about flying rods was in reference to a very well studied subject where "bugs" were seen in video appearing as very fast moving streaks of light thought to be 4th dimensional. After exhaustive study they found that the cause was shutter speed, bug speed and lighting. Speed and perception were greatly exaggerated when looking at the video.