If Johnson wins in UK, does that mean the population supports Brexit?

Not necessarily because even some in the Conservative party don't support Brexit. Conversely, some in the Labour party do support Brexit.

We have to wait and see the final tally and who made it in to determine what the prevailing sentiment was.

No, because he’s unlikely to get much more than 42% of the votes cast. But that could give him a majority in the Commons. And aa R1 said, support for Brexit isn’t the only thing determining how people vote.

No, it just means the British people are as stupid as the American people.

No, OP. The referendum means the population supports Brexit.

Brexit's happening. And it took two votes because some refused to accept the first one. I honestly believe we would have had a labour government if they'd have just accepted the referendum results.