UKBA says "To come to the UK as a family visitor, you must be able to show that you will be visiting the following family members in the UK:
spouse, civil partner, father, mother, son, daughter, brother or sister;
grandfather, grandmother, grandson or granddaughter;
spouse or civil partner's father, mother, brother or sister;
son or daughter's spouse or civil partner;
stepfather, stepmother, stepson, stepdaughter, stepbrother or stepsister; or
a person you have been living with in a genuine and subsisting relationship, like marriage or civil partnership, for at least 2 years before the day you apply.
If you want to visit a family member who is NOT LISTED ABOVE, you should come to the UK as a GENERAL VISITOR."
I therefore considered UNCLE as General Visitor and not a Family Visitor.
Anyway, rules are always complicated. It's how we filled the application form and how we presented the evidence that matters most.