It’s a telephoto lens so anything moving in the foreground is going to appear to be moving faster. Here’s the entire video that you can step through or play in slow motion. Other birds or insects can be seen flying around before the explosion.
http://anilyzer.com/?page_id=7&type=youtube&vId=_BgJEXQkjNQ#playbackRate=1&seekTo=0
I saw birds flying around, and a few fast insects. But nothing like what appears one second before the rocket explodes.