That's the point. The value of a company is determined by the price that people are willing to buy & sell its shares at, but you don't have to be that person.
The VC fund in the article is basically saying "We believe that anyone buying late-stage startups at these valuations is a fool and is unlikely to get a better price when it goes to the public markets, and we are not going to be the greater fool with your money."
The VC fund in the article is basically saying "We believe that anyone buying late-stage startups at these valuations is a fool and is unlikely to get a better price when it goes to the public markets, and we are not going to be the greater fool with your money."