I'm trying to understand the use of the word 'moments'. It seems the article, which is clearly biased in favour of the security researcher, is trying to downplay the actual event. It is hard to really grasp exactly what happened here because the amount of time that the posting was live is not specifically mentioned. Generally, I would assume moments is about 10-15 seconds or less. However the following happened in those 'moments':
1. The issue was published
2. Somebody realized it was published in error (there is no indication of who)
3. Groupon somehow found out about this being posted
4. The article was removed
So you can give the benefit of the doubt and assume it was an accident. But as a security research you have to realize that making this sort of mistake can have serious repercussions. If Groupon somehow discovered it had been published, it isn't that unreasonable to assume that others had as well.