I'm kind of glad there isn't any onboard video of me back when I was road racing, I was probably sawing on the wheel a lot more than this guy.
According to the video title he was on a qualifying lap, so presumably he was pushing it as hard as he could. Also, it's a car with 1960s chassis and suspension design so it's not going to be as sure through the bends as an equivalent modern sports car. I don't know what kind of rubber compound they'e allowed to run in vintage racing either; the tires are probably better than what was used 50 years ago but I suspect they aren't nearlyas sticky as what is used for modern sports cars.