You're mistaking the clams of a politician/political party with the law/constitution.
No, I'm not. The pamphlet was issued by the leader of HM Government. Whilst he was a politician, he was not writing on behalf of the Conservative Party, but as the Head of HM Government. It is simply not good enough to say that those within Westminster knew it was advisory. The Government clearly stated that the result would be enacted.
The unambiguous message was "You vote and the majority will decide". That is a contract as far as I am concerned.
HM Government is NOT Parliament. The head of the Government can say what they intend to try and do, but Parliament is Sovereign, and can vote down anything that the Government wants to do. Most of the time the Government has a majority in Parliament, so they tend to be seen as being the same thing, but they aren't.
The leaflet should be read as "You vote and the majority will decide" followed by "In the event of a leave vote The Government will (try to) take the actions required to remove the UK from the EU". The first of those actions is to pass a bill invoking Art50 through Parliament, but the Govt cannot force Parliament to vote such a bill into law if a majority of MP's decide to vote against it(which they won't). Allowing the PM to invoke Art50 without the approval of Parliament has been ruled unconstitutional, and I fully agree with that decision.
So again, in the UK "Parliament" is sovereign, not "The Prime Minister", or "The Government", or "The People". That is a contract as far as I (and the constitution) am concerned.