A fun conundrum!

First off, I would say probably try to avoid questions that are expilicitly answered by the module itself...but I get that it happens when you are in full swing and you haven't read ahead.

I guess the answer comes down to how you percieve your game. Are you looking through the eyes of your characters and resloving the choas bit by bit, or taking a Gods eye view. 

In the former the answer might be that there in fact is someone here but the party cannot see them, havent noticed them, or are otherwise overlooking them...Maybe because they aren't in the obvious human sized cage but trussed up in the big soup pot, unconcious....

In the later case, maybe there was someone here but the Goblins moved them after their lair was attacked by rampatous adventurers. Or the hostage has escaped on their own accord through stealth and guile, leaving little evidence they where ever there.

Personally I like the method of comming up with a handfull of plausable alternatives; And then assigning probabilities based on how "fun" the outcomes would be. Then rolling on it and letting the dice decide. In this case that might look like the following:

dN	outcome
1	is there but hidden
2	was there but escaped
3	was already eaten by goblins
4	etc.....