Robots have many means of detecting a WordPress site (usually simply just try things) and almost never rely on the footer signature for detection.
Even the article you indicated states this:
Here are other reasons that may convince you not to use obfuscation to secure your WordPress website:
- Malicious robots don’t consider the version of WordPress.
- There are many ways to know that you are using WordPress.
- Any hacker able to access your website will eventually find information that you forgot to hide.
- If obfuscation was the solution, we would have no version of the products available on the market.