He seems to be saying "types are just a formal system; they are meaningless until given meaning by an interpretation". Which is, of course, true. But the same can be said of programming languages. They're just meaningless squiggles until interpreted by human or machine.
Assuming you have some sort of specification for your program, you can use a formal system (such as a static type system) to describe aspects of the specification. It's up to you to correctly model the requirements in the system, but it's similarly up to you to model the requirements of the system in your (far larger and more complex) program. The types ensure that the program fits the aspects of the specification you were able to describe with them.
Assuming you have some sort of specification for your program, you can use a formal system (such as a static type system) to describe aspects of the specification. It's up to you to correctly model the requirements in the system, but it's similarly up to you to model the requirements of the system in your (far larger and more complex) program. The types ensure that the program fits the aspects of the specification you were able to describe with them.