I am certain this is not true. They have been making the 2020 cars with Grey Performance wheels since at least 21 October! I know, I have one scheduled for delivery in Australia in two weeks. Already invoiced (that’s why I can confirm build date, model year, wheels etc). It is currently going through clearing in country. It takes approx 7-8 weeks from manufacture date to delivery in Australia.
Now it could certainly be the overseas were prioritised for the 2020 builds as it is well know Tesla has learned its lesson and wants to minimise cars in transit at the end of the quarter. So there may not be many 2020 in the US (we know there are some as we saw the truck). I also have no idea what he saw in Florida. My only point is the factory is turning out 2020 M3P+ with the grey performance wheels since at least 21 October. The first deliveries of this model will start next week down under.
Here is a link to a pic of one of the first 2020 Performance with Grey wheels that has been delivered in Sydney. Keep in mind this car is now in customers hands and was built in mid-October (just takes 7-8 weeks to reach customers in AU).
Pics of Model 3s with the new grey performance wheels