Hi there, and welcome.
An 'outside influence' essentially means some factor not due to a fault in the manufacturing process.
These can include; bird droppings, airborne pollution, solvent damage, stonechipping, etc.
It's impossible for me to say what's caused it, but I can understand why you are so aggreived, given the age of the car & the care you employ.
It is possible for you to appeal their decision, or for
Renault Customer Services
to offer assistance.
What you may well have to do to obtain this, however, is to arrange for an independent inspection (which you have to pay for), on the basis that if its a Renault blame, then they cover the cost of repair, plus the inspection.
My only concern is why only a small part of the bonnet has shown this defect - if it were due to a manufacturing issue, I'd be inclined to think the entire bonnet would be showing this finish?
And if, as you say - you clean the car weekly, then you'd have picked up on any other areas showing problems.
Is it possible that some form of malicious act could of caused this?