I think they have algorithms they're dealing with.
The smart meter is looking for rises in usage minute by minute, or maybe even second by second.
It can "know" what you're using based on how much draw and what kind of duration. And time, frequency, etc
Water heater and dryer have similar draw, but not the same duration. And not the time, really. Water heater will be very regular, almost on a schedule throughout every day.
Dryer might be run a while, maybe even every day, but not over and over every day like a water heater.
It won't matter if it's 120 or 240, that meter and the accompanying programs, will know what you're using.
They even have your bath time down to the minute