When it's arguable that this was just a really bad timing for a movie like this, what with three hurricanes and a horrible mass shooting, and people definitely weren't much in the mood to watch a pretty high concept science fiction movie, I wouldn't say that the movie bombed, but that people just didn't feel like going to the movies.
I'd say it would've bombed had there been some other movie that absolutely crushed it in revenues. But there wasn't.
In any case, they'll get their money back eventually, no doubt. These opening weekend figures mean jack anyway. Also, isn't it the case that quite a few legendary movies had really horrible box offices, and ended up being legendary anyway.