To clarify things a bit. In module Whatever you are only defining one function do_thing/1 which has two clauses. While it looks 2 separate functions they are actually parts of the same function. In the modules Foo and Bar you are defining 2 different functions do_thing/1 so now you have 3 functions do_thing/1 in separate modules. What uniquely defines a function is the module its in, its name, and its arity (number of arguments). Importing does not change that, it just gives you a way of not having to prefix calling a function in another module with the module name. You still have 3 different do_thing/1 in 3 modules.
