They almost certainly use software written by someone else either at work or at home. For example, they likely use an IDE written by someone else. As such the

They almost certainly use software written by someone else either at work or at home. For example, they likely use an IDE written by someone else. As such they are "users". It is quite common for self-proclaimed "developers" to write software for other "developers". In other words, developers who are "users". We see this on HN everyday.