I suspect that there was something flying through the frame, and it flashed a strobe twice. If the strobe pattern was two quick flashes, then a pause, then two quick flashes, and so on, then it might have been in the frame only for the flashes that you caught. It could have been an aircraft anti-collision light, but typically you'll also see streaks to correspond to navigation lights, which do not flash. And in some cases where I've caught anti-collision lights, they also lit up the under side of the aircraft, making the nature of the light obvious.
For what it's worth, I've seen (visually) lots of flashes in the night sky over the years. Most of the time - but not always - they are in my peripheral vision. When I catch them, I always look for the source, and often times, I can't see anything else and no repeats of the flash. Sometimes I've seen one or two more flashes and then nothing. I've wondered on occasion if I'm just imagining them, or if there if they are artifacts of my own vision - but on a few occasions, I've had another astronomy next to me ask "did you see that", because they saw the same thing.
I'm sure that there is a perfectly reasonable explanation, but I don't know if there is enough data in your images to tell anything for sure.