You might be confusing license with access. The product itself has a proprietary license. Even then, a majority of the libraries they produce are also available under the MIT license.
"source available"[1] is a different thing, and you're right that this project is "source available".
[0]: https://opensource.org/osd
[1]: https://en.wikipedia.org/wiki/Source-available_software
Their EULA forbids distributing the software, hence not open source.