Screenshot of settings in the Timelines tab. An option called "Automatically fetch remote media when they are not available" is turned on.
https://storage.gra.cloud.ovh.net/v1/AUTH_91eb37814936490c95da7b85993cc2ff/tootfedilabapp/media_attachments/files/113/647/518/018/679/595/original/c58674f200578b68.png