Everything in life has different odds of happening, and when lower odds materialize, we call that "luck".
There are a number of comments saying very similar things to the top voted one: so it was indeed luck that their comment floated to the top among the many others. Perhaps they were there right when the story was posted (luck, right?) Perhaps they used exactly the trigger words that made others appreciate the comment (luck, right?).
The fact that there is a luck element to many things does not mean that those are unworthy pursuits. And it's ok to acknowledge the luck factor when it can dominate the results (i.e. you wouldn't talk about a lottery without considering luck).
It definitely is. Just because success mostly boils down to luck, doesn’t mean that people realize or acknowledge it, which leads to unhealthy obsession with “being successful” that permeates the society.