Actually all it means is that the released segment started 6 seconds before he used the turn signal. What went on before or afterward is not relevant, and was not posted. I imagine it records continuously and either overwrites old data or he changes media. Otherwise it would not have action prior to being stopped and harassed, which is surely coming.
Brent claims the tape is unedited, and that does appear to be the case. The perp's (that is what he is) lawyer has said something about wanting to see the entire tape.
Sure, that's possible. And the sounds of hoofs could be zebras, not horses.