The passage from AFFC is forshadowing that Aegon is not a Targaryen but a Blackfyre. The black dragon pieces tossed in the river are the Blackfyres who went over seas at the end of the Blackfyre rebellion. One of those black pieces washed back ashore on Westeros though....and rusted red. A Black dragon piece rusted red. A Blackfyre turned Targaryen (red is the color of house Targaryen. Strong evidence supporting the idea that Aegon is a Blackfyre and the Mummers dragon.
Only click this link if you have read through book 5...and if you have only click if you want to know the truth about *spoilers in white if you haven't read book 5*
I don't think there's anyone who's read the books and knows the back story that doesn't think Aegon is really a Blackfyre. The inclusion of the Golden Company all but confirms this. Where was the description of Illyrio's wife in the book? I'd be interested in reading that again, I remember there was a statue but I thought it was a guy.