Yeah good question. To add to the confusion, this paper published PNAS says "2.83 ± 1.0 t of CO2-equivalents per capita". Per capita is different from per household but might be a better metric
It also states that using just national energy statistics (this study actually analyzed 93 million households instead) you'd arrive at 3.19 t CO2 per capita which falls in line with their results
And, either way, this maneuver seems like it generated CO2 emissions roughly equal to those that would be saved by 10 people line drying their clothes for a year. Which 10 people are we gonna pick?
https://www.ccfpd.org/Portals/0/Assets/PDF/Facts_Chart.pdf