I had a look at the log and video below my thoughts:
Your video ends when you yaw 180 deg. This is at 365 seconds into the log. your video is 21 seconds long, so starts at 344 seconds.
@344sec: you are cruising at ~4m barometric altitude, or 5.1m ultrasound altitude. you are at full forward elevator, but there is no throttle input.
@348sec: Still at full forward elevator, and no throttle input.There is a small drift in altitude barometric altitude to 4.7m ultrasound altitude still at 5.1m.
@352sec Still at full forward elevator, and no throttle input. There is a small 2 second decent to 3.6m barometric and 3.9m ultrasound altitude.
@354sec You give full power, reduce elevator to 0, and climb to 10.5m barometric and outside ultrasound altitude.
@360 you start to yaw 180 deg as we see in the video.
This all seems very minor. but I agree your video appears to show a bigger decent. so I looked further into the logs:
@344sec you are cruising at 6.6m/s in the next 10 seconds this gradually increases to 9m/s that is a significant increase in forward velocity. The increase in forward velocity gives an impression of flying lower, I suspect that this combined with actually drifting a bit lower resulted in what you experienced.
Your reaction was fast and accurate
.