[derekp7]

The answer to your question is simply linguistic shortcuts. That is, the question could have been phrased such as this:

"I am but a casual reader with an interest in this topic. I have read about Gravitational Lensing, and the pattern matching algorithm in my brain finds a loose match between that an this phenomenon. I am curious as to the particulars of this that makes it different from what I've read before, such that this requires a different explanation".

Of course, that is way to many words, an the shortcut of "Why isn't this Gravitational Lensing" is a more succinct way of asking the question. Which is a major reason why HN has as one of their guidelines "Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith. "