I can think of a wide variety of topics to bring to 5th graders to make them think that don't require giving scientifically faulty information as fact and challenging students to think and research on their own, particularly without those research skills or tools. Anything from a debate on paper towels vs washing cloth rags (paper generation and transport but providing timber jobs vs water use and personal labor) to War on Terror ( wades into politics, but kids at that age can consider the risks of traveling vs TSA privacy issues vs fighting wars abroad for security here).
Suggesting topics that are not scientifically defensible is not making them think. It's giving kids faulty information and hoping they'll figure it out. Honestly, given the conversation you related, it sounds like he's covering for himself in response to getting caught.