Differences to the fluid_styled_content documentation

[DenisMir]

I'm comparing this content element with the guid that creates a content element in the fluid_styled_content documentation. Why are the TCA configurations and addition to the CType selection so different?

\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPlugin vs \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTcaSelectItem. Or why are the TCA definitions not in the file ext_tables.php?

I'm just trying to understand the differences since I'm searching for the right way to implement content items from now on.

Thank you very much!