It is not a lie. The idea is that Tesla would go out of business and a vulnerability in the car would be found and exploited to kill you in the absence of security updates. Similar to how the article says:
> We're guessing a Charter alarm would still be able to make loud noises when someone breaks into a house, but that doesn't mean it'll work with an alarm-monitoring service.
What lots of assumptions? that's a single inevitability that a self-driving car manufacturer, Tesla or otherwise, will go out of business, rendering the car offline only (the point made in the article) or worse, like the case with Android phones, you'll have plenty of vulnerable cars on the street and some community updates (like the work of LineageOS for instance).
It's the same point made in this computerphile video[1].
> We're guessing a Charter alarm would still be able to make loud noises when someone breaks into a house, but that doesn't mean it'll work with an alarm-monitoring service.