Yes, it is. Its basis was developed independently, but when people speak of the STL today, they are referring to the standard algorithms and containers.

The containers for the standard library are indeed at the link you provided. Those are traditionally referred to as STL containers. No?

The STL is a product developed and maintained by SGI. If you look at the containers listed in the article and on the SGI page, you will see a different set than is present in the C++ standard library, especially if you discount the containers that weren't in the C++ standard library when the article was written.

Now, people often refer to the C++ standard library as the STL, but the author of the article was clearly confusing the STL itself with the standard library, not just the name.