I buy a lot of tickets on United's website (formerly Continental's), and it isn't a great experience – but the idea that this list is the flight's passenger manifest just doesn't make sense to me.

The screenshot shows the point in the ticketing workflow where you give the name (and basic TSA-required details) of the passenger purchasing the ticket. If you're logged in to the website, you can add as many passengers as you want to your account, which might be handy if you purchase tickets for your family or for coworkers. My guess would be that somehow the session got into an incorrect state and is showing the passengers from one or more other accounts.

Also, the form is the same whether you're booking a one-way flight with one manifest, or a roundtrip with many connections where each flight has a unique manifest. I don't understand how the system would be able to deal with these diverse sets of data.