Proof of purchase is not an issue. Item being new is not an issue. The fact that it was not purchased from a B&M store appears to be only issue however that was never disclosed.Just because the item was sealed in a box doesn't mean it came from the factory that way and the maker is free to require proof of purchase.
By the way, Grill has to be assembled by hand, all the parts were sealed in plastic bags down to the last nut, bolt, etc.. BBQ Grills get very dirty and worn, its pretty obvious when it has been used however that fact that its new does not seem to be an issue here.
The issue at hand is if they can make up terms not disclosed in the warranty information after the fact to reject a claim or if there is legal basis for a lawsuit against them.
If Ford tries to void your car warranty for getting your car service from a 3rd party place( a non-ford authorized dealer), the law said you can fight them on that.
Question is if you can take the same approach in this BBQ warranty situation which is the information I am seeking.