The phrase "turnip truck" is an expression used to describe someone who is naive, gullible, or easily fooled. It suggests that the person just fell off a truck full of turnips, implying they are not knowledgeable or experienced. Full definition
What turnip truck did you fall off of? (cfact.org)
«I didn't just fall off the turnip truck. (usatoday.com)
So for them to think a blogger who has allowed discussion on the issues surrounding Tony as a public figure who used his privilege to control — is going to take it down blog posts simply because those who support the NPD or the NPD himself claims the «court» says so, must think we all fell off the turnip truck. (nakedpastor.com)