I agree with you that this would be the safer route. For a production file upload service, file uploads should ideally stored in a specialized blob store, e.g. Amazon S3 or Google Cloud Storage.

However the PHP code was written as easy-to-use sample code and I did not want to introduce a database as dependency and keeping the sanitized filename plus extension keeps the meta information intact.

If I had provided better information about how to securely configure the Webserver to allow all file types for upload, using the original - but sanitized - filenames would not be an issue.