Before the 5.90 release, remote (i.e.: external) images used in pages' body (e.g.: !(https://example.com/image.jpg)) were systematically fetched and stored locally, in _sites/assets/ directory.
However, this is not a behavior that Cecil’s users want systematically, that's why we added an option to disable it:
Option to disable auto-generated favicons in the metatags template is now working