I think it was strategically coined to avoid the term "second referendum", which is actually what it would be. However, for those who cry "foul" or "undemocratic" you could quite realistically say the first was a simple binary choice, "Leave" or "Remain"? There was no explanation of what this would actually involve, i.e. customs union, WTO rules, Irish borders, effect on businesses, and - today - the news that security forces were being put on alert to deal with the effect of a 'No deal'.
Quite early on it was decided that Parliament must have the final say on any future relationship with the EU; now that we know that Parliament will reject May's deal, leaving a choice between No Deal or No Brexit, it makes sense for the people who voted in the first, to have a say on how things should go from here.
Personally I blame the 1975 referendum, as it established it as an acceptable procedure to decide on Europe (but nothing else, unless you're Scottish).