Anything you pay for (directly or indirectly) should be of acceptable quality.
Obviously there is a big problem with this bread, just because it is GF doesn't mean you shouldn't expect an edible product.
Some may remember Genius were the company who released gluten-contaminated so-called GF bread to supermarkets.
That was because of human error.
Their GF area is just part of an ordinary factory and I understand a gluten ingredient ('white powder' ) destined for the ordinary baked goods was delivered to the GF part of the factory and used in what was meant to be GF items
I guess another human error might be responsible for this problem?
BTW if you can get Sainsburys own brand fresh GF bread (as recommended on here by lots of people) that is very nice, your son might want to try that.
It is unsliced but easily sliced. I have eaten it two days running fresh and then sliced the rest & frozen it.