Buzzatronic
I think in your situation I would do the same thing. A 10mph differential is really not much, but the distance was definitely questionable. Since you have it recorded, make sure you save a copy. That way if it happens again, you have proof that it's not just a random occurrence (especially if it's the same car).
I'm lucky to have not experienced a near miss, but since most of the roads I'm on either have ample shoulder or are not heavily traveled, that chance is decreased further.