The first part is an impossibly broad definition of chelator. This is made clear when the initial chelator they mention is acetic acid. I suppose just about any acid or alkali would be a chelator by this definition, including ascorbic acid.
We are discussing mercury chelation. Here is a link quoting a scientific study disproving mercury chelation by Vitamin C.
Btw, you can find a lot of things on the internet, particularly when it comes to Vitamin C. You can show that Vitamin C can cure just about anything with some quotes on the net. You should stick with findings that have some scientific weight.