"Should the Brexit referendum have allowed citizens of the rest of the EU to vote?"
Not quite the same thing, jno. Not quite the same thing at all.
The EU is not (yet) and independent sovereign nation and citizens from other EU nations should have no say over the affairs of another member state, even if it is associated with EU membership. But more than that, there are not vast sums of EU taxpayers' money being shovelled across the English Channel every week to support the UK (quite the reverse in fact). In contrast, huge lorry loads of English tax revenue head up the M6 every night to fund the outrageous "Barnett Formula" which provides about £2k per head per annum more to the Scots than to the English. Successive governments have refused to do anything about this iniquity and, as a result of the Westminster government's largesse, the Scots now have their own spending plans which enable them to provide "free" goods and services which English taxpayers have to pay for.
The question is not simply that of Scottish independence but also of Scotland's membership of the United Kingdom. It is not unreasonable, therefore, for the entire UK electorate to be asked if they want this blatant unfairness, which has only been exacerbated by devolution, to continue.