Mirroring iPad issue. Please help

I recently visited the apple store to discuss how I could use my iPad to mirror. He asked if my projector had an hdmi slot, which I said yes. I explain my room setup and we discussed that I am unable to creat an wi-fi network and that I cannot place personal devices on the network. He told me my only option was to buy an apple tv and that the cable models will not "truly mirror" the iPad screen unless the app is designed too. I'm not sure why he pointed me in this direction if there was no way to mirror without a wifi network. I have the AT&T model, did he forget to tell me a step that I should know about?