I noticed a spike after the smart meter was installed...
One account that I have had for 17 years always had no usage... just paid the minimum
The ONLY load was from a very small sprinkler transformer.
When the smart meter went in I started to show a couple of kW each month... nothing changed but the meter... I'm guess it is much more sensitive to minute loads?
At the cabin I would have everything off and still recorded minute usage... last summer I opened the knife switch below the meter and no usage now.
A small transformer as you mentioned is 5-10 watts, depending on the load efficiency, etc
That would be 3.5-7 KWH for a month. It is likely true as you mentioned that the newer meters are more "sensitive" and better at measuring small loads. Looks like you got away for years "slipping under the radar" with the older mechanical meter. Bearing and gear friction was often greater than the available driving forces at very small loads, with it worse as the meter aged. People complain but it is likely more accurate today to the dismay of the complainers.
paul