It's difficult to see how someone who's had a consistent position for years can be described as "flip-flipping". Ah, well.
As TTT says -- it may be a technical point, but since we are arguing about the definition of democracy, the technicality matters. Had the Libdems won the General Election then the public would have endorsed their position, and so it would have been democratic. As we know, they did not, which puts an end to the matter -- until the next election, when they or any other party would be free to put the same policy back to the people and see if, this time, it would be accepted. And so on. That's how democracy works.
By contrast, the insistence that any given law or vote or whatever is binding in perpetuity and can neither be questioned nor overturned by democratic means is obviously, by definition, anti-democratic. It takes away power from the people of today and hands it to their past selves. It may well be that the country of today agrees with the country of 2016, and would reaffirm that result if asked today -- but there is never anything anti-democratic about asking. After all, what if we *had*, as a nation, changed our minds?