As I mentioned, your figures are from a Solar PV seller. Designed to be low, to make the other calc of $ and panels much better. Those averages are about right for me. BUT I have gas cooktop, solar HW, so if I did not have these, it would be higher.
I just checked a few bills and I reckon our household average is around 800-900kWh per month, with a mixture of electricity and gas. That's a family of 4, three heatpumps, mostly LED lighting and efficient appliances. So 30kWh per day, maybe 25 in summer.
I think you'd have to have a very efficient house and/or like wearing warm clothes to get it down to 18kWh.