@kbern I've had one single nose dive from when I've gotten my board about 3 months ago. and I quickly found out that the most vulnerable point of the board is acceleration.
If you try accelerating the board faster than it can handle, it will nose dive in some cases.
Ever since that one nose dive (which ended up in me bruising my elbows a little), I've started paying close attention to my acceleration and I've been fine ever since.
If you're saying this happened when you were accelerating to over-pass these bikes, it sort of makes sense.
Basically, While I am aware that this is not scientific and I am merely basing this off of my own experience:
Accelerate gradually. Push too much and it may end up bad ;)
@fabuz looking at your slow-mo you can see that your foot is not touching the pressure pad at the front-end.
This may sometime cause issues where the engine dis-engages as if you were trying to dismount from the board.
This SHOULD happen at very low speeds (in order to dismount from the board), but I've had this happen once or twice at "higher-than-low" speeds, so it may be the same case here, where the board 'thought' you were slow enough to disengage and detected one pressure pad was not pressed, and so it stopped the engine.
This is also supported by the fact you managed to easily recover on foot, which usually does not happen on higher speeds due to the body posture when riding the board (sideways).
It has (fortunately) never happened to me at high speeds.
Hope this helps !