Afaik, that was a decision of the people who live in Crimea on the referendum. It is like Brexit or referendum in Scotland. For example, now UK leaves EC, so in the same way Crimea has left Ukrain. It is how democracy works.
2. Constitution of Ukraine states that only citizens of whole country and not locals can decide such questions, _ANY_ local referendum regarding sovereignty is illegal.
So NO IT IS NOT LIKE BREXIT or referendum in Scotland. Ukraine is unitary country.
We detached this subthread from https://news.ycombinator.com/item?id=12066283 and marked it off-topic.