They, like you or me or anyone, may have been tested and found positive before the accident. It’s also possible that in the investigation it was discovered that they had been having symptoms at the time of the accident. The ME may have then tested first Covid (or presumed them positive depending on the story). I can imagine that someone who was very sick (to the point of needing help oxygenating) may have been trying to drive (to the hospital for help or to the liquor store for their usual daily fifth of vodka) but lost consciousness and crashed.
Alcoholics can get Covid, too... and they’d make especially poor drivers.
Or, it could not be true (not the the OP is purposefully lying, just that the "broken telephone" ends up with a false story or some in the chain is purposefully lying).