You really have no reason to post this here. If nothing else, you'll hit the programmer equivalent of the blue line. The people here will side with the developer reflexively. You literally have nothing to gain.
Consider it for what benefit to pigeon.ly? True there is altruistic value to the HN community, but from a business perspective his OP is likely to cause damage to his brand.
Not really. If the original poster hadn't outed them by name it would be fine, but as it is a very popular HN post directly says that Pigeon.ly are thieves. I think they're reasonable to want to counter that.
But he should say (if true) that they threw out the old code because of reasons, and rewrote it from scratch.
That was the biggest issue raised in the initial allegation: that they were currently using code that they had not paid for.