You should probably have read the rest of the blog post, because in Rust it is a compiler error to not test the result, and the post specifically calls this out. Specifically, look for this section:

    let mut my_file = MyFile::open(path)?;
    // Note the `?` above. It's a simple operator that asks
    // the compiler to check whether the operation succeeded.
    // The *only* way to obtain a `MyFile` object is to
    // have a successful `MyFile::open`.

    // At this line, `my_file` is a `MyFile`, which means
    // that we may use it.