We all have in our life did a little of the I CAN get in front of you on the roads. Maybe not full on street racing but that other car pulls up next to you and you just get into the moment (road rage included). Poor Judgement is the perfect title for this. It is what it is.
A "street racer" can debate this if they like, but it is not their main job to race so in that they do not have the experience to be competent in the act.
Many variables probably went into this accident. road conditions, tire conditions, drivers condition (state of mind, sobriety, etc), condition of the Mustang itself.
In full disclosure. When I do a mod/upgrade on any car that I am working on. I know of an area that I can open it up on. It is a local well know Drag Spot that has no residential traffic, no houses, pretty much nothing but a Bridge that is 300 ft and has a straight away that is more than 1/4 m. The Local Police know about this and have allowed some testing and tuning of single vehicles in the area but will not tolerate competition. I also head to the expressway.