An average EV gets what, ~3.5mi/kWH? An average US car does ~12,000mi/yr. That theoretical average EV would then use ~3.5MWh. Two would be ~7. But this author is in the UK, where the average car only does ~7,500mi/yr or so or a little over 2MWh/yr. So for their two UK cars, assuming they drove an average mileage in an average EV efficiency, they would likely have used something like 4.3MWh/yr for their cars. About 20% of their total electricity usage. This drops a good bit if they're really getting closer to 4mi/kWh in efficiency, which is likely if they're not driving on many highways like one does in the US.
We have one car and charge it quite often.
I just checked last month: 184kwh went into the Leaf. We used 557kwh in total (excluding the car charging).
We generated 1170kwh.
The key thing for me is the wild energy usage from the house. It’s a lot.
Edit: Your car energy usage calculation works out awfully close to what we use.