This makes since, but I do like the idea presented before you, that humans are natural, and our evolution is natural, therefor the things that we make are natural too. But then where do you draw the line? If an alien drops a new element on earth, would this then be not ‘natural’? Or is it impossible for anything to not be natural?

Except the definition of natural is a human made concept which means "anything non-human made/consequence" ;)

We're part of nature and so everything we do is occurring there. Is the real distinction things that wouldn't exist without human intervention? So, like Teflon and plumcots wouldn't be natural but water and plutonium are.

Things that aren't naturally occurring would be supernatural, no?

That's the original meaning of "artificial", something that occurs through art or skill. Humans have always distinguished themselves from the rest of nature, it's part of that. It's not a useless distinction, but it breaks down when 'natural' is considered healthy or otherwise good, and 'artificial' unhealthy or otherwise bad, when that's a non-sequitur.

Now we're arguing semantics. "Naturally occuring" in English means not synthetically produced / found naturally in the environment outside of human influences.