Well, that's sort of my point - as written, this is not something the goblins do. You can, as a DM, use a bit of foresight to anticipate that the information given isn't enough to give the PCs an idea of what exactly was going on, and then embellish or add interactions to compensate, but this is not something that the adventure itself explicitly encourages. This is a clear example of something being written for the reader, rather than for the DM or player. The PCs experience the barest shell of this interaction and are unaware of the full story. The DM does not have the chance to explain (without stepping out from behind the 4th wall) what exactly has occurred, but the reader knows all of it.

Just because it's printed on the page, it's not expected that the PCs will know it. Perhaps it's purpose is:
A) To highlight the fact that while goblins are wicked, evil creatures, in Golarion they're to be played up as comical misfits & generally speaking - batcrap crazy as well.
B) Give the GM a chuckle as he/she reads.
C) A & B
Hell, there are plenty of things in your average adventure that PCs might learn through the course of the adventure. That doesn't mean that if they get to the end of the module, they're guaranteed to learn everything that they module says is possible for them to learn.
Seriously, does the module HAVE to specifically encourage a DM to do something? As a DM, I can play a module straight as written or I can make it my own by adding, tweaking, etc. as others have mentioned. If the publisher gives me snippets to riff off of that's a FEATURE not a flaw.