Not sure the sources, but I would not be surprised if it is 1g/lb for athletes, or 1g/lb of lean body mass, as someone mentioned.

For the general population, 1g/lb is way too much.

It's an error that has been continuously repeated in locker rooms after Americans misunderstood what a kg is.

Sorry, but while the meathead stereotype is probably not entirely unfounded, I guarantee that 1) I don't get my information from locker rooms and 2) weightlifters are plenty familiar with what a kilogram is.