Rising / falling premiums are a possible factor of at least two things:
A. A bod’s recent claim record; though some (many?) have found that their premium did not increase after a claim
B. A generally rising or falling ‘market’, maybe distorted to some extent by region and / or make of vehicle and insurers’ individual appetites. For example, it is common knowledge that London is now less popular with insurers than it was even a year or so ago. Bikers have played their part in this, too.
Your friend will know when he next applies for insurance.