I believe the Brexit votum succeeding had the same reason as the first smoke-banning referendum succeeding in Bavaria: those opposing had thought their opinion to be "mainstream" anyway and didn't care to go vote while a small but loud minority actually brought their people to the booths.

I believe that similar effects caused the vote of the Orange as POTUS...

The political situation is quite different. The UK had for long a very negative public opinion about the EU, fueled by politics and the press. It was for a long time on a trajectory which brought it into the brexit situation.

People like Farage would have not accepted a failed referendum and would have worked harder to influence public opinion to leave the EU. Thus leaving the EU was not a surprise decision because some voters did not show up, but based on a decade of politics.

I agree, yes, especially that the yellow press has fueled EU-skepticism is a worrying trend, which is also visible in other EU countries.

However, the referendum was 51.9% Leave, with a turnout of 72.2%... it could have been shot down when more Remain-ers had bothered to vote.

This would not have solved the problem. The exit would have come only a little bit later.