What he’s saying is that anything that creates downforce (or lift) is also going to create some drag. The hand out the window is a good example. Also look at racing, its always a delicate balance to get as much downforce as possible with as little drag as possible.
Back on topic, if you want to push your car to 150, do so in a controlled enviornment (track). Don’t do something like this anywhere there might be a chance of an innocent bystander getting in the way. There’s enough tragedy on the roads as is with people not able to controller their cars at normal speeds, don’t add to it.