They were talking about lighting a small candle. That just does not put out a meaningful amount of heat compared to the risk of knocking it over and setting the interior of your vehicle on fire, especially if you will be sleeping. Every year people die trying to keep warm in emergency situations or non emergency situations.

To be safe, eat food before you go out on the road, bring calorie dense snacks, and bring way more warm clothes than you’d think you’d need along with whatever other gear you need!