Well, they left you capture "the moment", which is just a posed shot in fact. Then, after you captured it, they begun the usual habit. If they had prevented you from taking your picture, that would have been bad. After that, I would have gone near the couple and took a picture of all the crowd taking a picture.
I'm not surprised she said YES, people don't stage all this to say NO. (We don't have "proposing" as an event with a photographer in this country, but no doubt we'll have it as soon as the voice reaches here that in America they have).