Sorry, can't see anything dangerous until maybe the final spurt away from the roundabout, even with the undertake there was plenty of room. Clearly the unfortunate rider was not expecting the fiesta to overtake & must have let his level of concentration drop, (probably, looking in his mirror to see what progress his mate was making having just undertaken him) otherwise he had plenty of time & room to either brake &/or thread between the fiesta & the other car.
Who's to blame...the rider is & always will be at fault! (& I'm not trying to be sanctomonious) because you really should always expect the unexpected & ride with full concentration & the awareness that every other idiot is out to get you (unfortunately none of us do or there would hardly ever be any accidents).
Every near miss & accident I have ever had (incl. 7 car write offs, plus 1 motorbike & 1 JCB (don't ask)) I could & should have avoided...

just don't tell my insurance company though..
Its alright I am safe to ride with...

my last accident was nearly 12 years ago now; just went through a little phase in my 20's...
Sentencing...well it wasn't his riding that caused the accident or played any part in his mates death, as for dangerous, that is subjective & depends on your own ability & the way you assess risks, I suspect the judge felt he had suffered enough with the tragic loss of his mate.
Have fun, but ride safe.