He is right though, in that most people (on both sides) didnt really consider the Irish situation when casting their vote. Most people who say otherwise are probably just lying.
In terms of its impact now and whether you should care about it or not, of course you should. But conversely, its not something that directly affects most of the voting population (in their eyes) so its not really at the top of their priority list when it comes to Brexit. It is however, a strong and convenient argument that remainers can use - but honestly if the sides were reversed, im not sure there would be that much difference.
To put it another way, if it transpired that the only way to maintain the GFA was to leave the EU, how many remain voters can put their hands on their hearts and say that that would change their vote? I dont think I can.