I find people conveniently ignore what they don't want to accept, even after facts are spelt out in detail from every angle, the evidence really rubbed in, they'll still cling to the smallest mote and insist on being right.
However, their own write-up on this poll is interesting, and indicates that people not voting in the referendum were split 50:50 a year ago and are now 80:20 remain, (whilst at the same time the graph there also suggests it's not just previously undecided people causing the difference).