No.
And from this info:
When we landed in clearly much warmer conditions (+5 degC in the car)
So it was below 5 C at origin, and likely below 0.
That means that even if the frost were cold fuel driven, and even if you were allowed "fuel frost" there, most allowances for frost due to cold fuel don't apply - because you can't know that it's not environmental frost, rather than fuel frost.
Oh, and I agree with FE Hoppy. I would have refused to fly, if I couldn't have got the crew to do something. (And arguably its my legal duty to do something - I'd hate to quietly walk off an aircraft I knew was unsafe, or likely to be unsafe, without warning anyone, and have it subsequently crash. Never mind the moral issues, I'm sure there are jurisdictions where I'd be flirting with a manslaughter charge of some kind)