TVPaint only supports linking sound, but not visual info. Everything you import into TVP becomes part of the file, which has it's own benefits and drawbacks. Benefits are, that you don't have to think about all those external files, that you have to carry on with your project, if, for example, you send your files to somebody else. Drawback is that if you want to update an image or a video, you need to import it again and again.
I guess that it could be a Feature request - to allow people to choose whether to create a linked layer from imported material... but please start a new thread about it
at home: Hackintosh Intel Core i9-9900K, GPU AMD RX 6600 8GB, Cintiq 22" + Dell P2415Q 4K displays, MAC OS High Sierra / Windows 10, TVP Pro 11.7.1 + TVP Pro beta
at work: Windows 10, TVP 11.7.1 Std https://vimeo.com/danas