It was worded as typical "promises" in politics are, so it's not totally unreasonable. And besides, shoving "I promise" in front of something political doesn't guarantee that such a promise will be carried out anyway.
Whether or not you see it as nonsense, it's vital that we hold the leaders of the Leave campaign to account for the way they sold their case. In many ways it was factually wrong, or extraordinarily arrogant or dismissive (such as Gove's "I think this country has had enough of experts" guff.) Whatever you make of this particular claim/ aspiration, etc -- well, firstly, it's obvious that at least some of the people who voted for Brexit had this in mind, so you've managed to insult people on your own side with that "half a brain" comments -- and, secondly, the point is that it fits into a picture of selling a vision of Brexit that is at best only an aspiration and at worst totally unrealistic and unachievable. Some Brexit supporters are still at the same thing today, in fact. I'd say it's pretty disturbing that you don't seem to care.
In the long run, it shows how poor our politics is that people leading the Leave campaign thought it was a good idea to try this and make something of it. It says a lot about how politicians on both sides see the electorate. They shouldn't be treated that way. I really hope that you can reserve your condemnations and accusations of nonsense for the Leaders of the Leave campaign (and the Remain campaign, in kind), rather than for the electorate.