*There may well have been mention of it, if you knew where to look but it certainly was not a main point in the campaign. Was it in the expensive pamphlet sent to every house, pointing out the whole issue would boil down to this border?
This was a referendum of the general public not a debate at the LSE. Millions of people are functionally illiterate. No one could honestly expect these people to go and do hours of research into the finer points of EU law?*
That's one of the strongest arguments against referenda. But it begs the question: should the people be allowed to vote on anything? That old elitist Bagehot was firmly of the opinion that the "ignorant multitude"* could not be trusted to make legislative decisions.
It's not the role of parliament to educate people and the power and partisan nature of the media would make it almost impossible. The Sun, the Mail, the Express could well have reported the complications around the NI border/GFA and Brexit in the way that the Guardian did, then more people might have been aware. But it seems they chose not to, and we can draw our own conclusions as to why.
Given that almost every statement in favour of remaining in the EU, whether it came from Stephen Hawking or the governor of the BoE, was dismissed as Project Fear. In the febrile atmosphere that prevailed at the time, I don't think people would have believed the complexity of the NI border issue had they had it explained to them in words of one syllable, with a map and a flowchart.
*Bagehot's expression, not mine!