Gastheracantha cancriformis is not a rare species

Or G. sauteri, that looks more probable.

I'm not sure if you're implying this is not a new species (which would be possible, of course) - but it does not look like either of those you mentioned. Not to appeal to authority, but the two members who initially called out the uniqueness of that spider have collectively identified thousands of Gastheracantha observations specifically, and never previously claimed that any of those were new species so far as I'm aware.

We'll never know, and this is exactly the problem with this kind of web pages. This is pseudotaxonomy.