That's not really true, is it? Coupling is independent from explicit code dependencies. Take, for instance, two programs. One writes to "/tmp/file". The other reads from "/tmp/file" but neither shares the code to determine the path ("/tmp/file", in this case). They're code independent, but very tightly coupled.
In fact, I'd hypothesise that copy-paste codebases are more tightly coupled than otherwise.
It's certainly true. Coupling measures the degree of interdependence between modules/functions/classes. If everything is copy/pasted, no module depends on any other -- it simply has its own copy of the code. This will result in a terrible system, but it will be very loosely coupled. When you change something, you won't have to worry about it's impact on anything else.
In your example, if the content of the file is changing the behavior of the program reading it, then the programs are sharing code via the file. It just happens to be going on at runtime rather than at compile time.
In fact, I'd hypothesise that copy-paste codebases are more tightly coupled than otherwise.