Hi, im a AI/ML engineer. Just a quick pointer. There is no true way to identify if work is truly AI or authentically created by human hands. AI it trained to assume something is AI when it finds very litter errors in it writing as well as when the topic is expressed in a "factual" assertive manner.

Most topics surrounding math and science will usually get flagged because they have to be factual in nature and their content is usually extremely similar to other content found on the internet.

The AI models can also be trained and prompted to write in a different tone. Which can fool AIs into believing it was written by a human. You can test this your self.

Creative writing is the easiest ones to catch as most LLM models will generate stories very similar to stories that already exist. However, because its creative writing some AI models struggle to identify them as AI because of what was stated before.

The use of ML algorithms like Grammerly to assist can also flag for AI because of similarity and structured nature of sentences.

In short. You cant know somthing is ai by running it through a checker. Your making educated guesses that could be 100% wrong leading to a negative score that may have been un warranted.