Porto not working for Portugal seems a bit weird. I looked up Vila Nova de Gaia and it seems to be a district which includes more than the actual city and is thus bigger than Porto but the city itself is much smaller
Also, the link you provided doesn't work. I'm curious about it as I didn't think Ecatepec was the second largest city in Mexico by city proper, though I could be mistaken.
Yeah, I think the source I used at the time wasn't very good, since that wikipedia page had some inconsistencies, so updating this quiz is something I might start working on soon
Thanks, and yeah I'll fix that when updating the quiz, it's those kinds of mistakes that I hate the most, since they are so silly but sometimes you just make them I guess