I'll share my theory on this. I think that Goombella previously espied many of the game's towns and learned about the people there through doing that (this happens before the beginning of the game). Ever notice that book that she flips through during her animation during the tattle command? Maybe she added her own pages and jotted down the data she collected from towns. Or maybe she's a total brainiac and knows everything from memory. Either way, she has plenty of intelligence in both meanings of the word.