When information shown by Trulia and similar sites is incorrect, it is because the data sources they are pulling from don't have clean data. For example, if your city's name exists in more than one County in CA, Trulia and others will pull schools data from both locations, even if you're trying to search by zip code. As a result, the system will show your local schools as well as others that aren't in your local area.
I've reported this to various data aggregators, and haven't received a response back yet. Seems they're searching more by city name than by zip code, and thus things get all convoluted.
Do report your situation to Trulia to see if they can get it corrected for you. It may be that they don't have enough control over the data to make the change, but at least they can investigate.