I know it seems irrational, but methinks he's getting clobbered because of the reputation of young Fiesta drivers, and thieves. We've seen something similar on Corsa renewals for young drivers.
"Duller" cars like the Mx5, of which I'm a fan, or anything less mainstream, may well be cheaper than the Fiesta beloved by us all. He might laugh but a Panda 100hp might be worth a look, or the smaller Japs. At the end of the day, they're not assessing him for risk, they're assessing people of his age who drive those cars.
Back to basics, he should try to include someone older, or a "girl" on the policy, even if they never drive the wretched thing. "Computer usually says" quote is lower with others on the policy.
That said, in any case, always try to negotiate, because insurance companies nail existing customers on renewal. It's called inertia pricing. If challenged confidently, they will crumble.