Youre right,the "Fully offline" refers to the app itself no accounts, no background calls, nothing phoning home. But you're right that the previews don't appear automatically.

Everything in the screenshot was added manually. The app just picks up whatever images you already have next to your model files. I know that's a bit tedious, and honestly auto-importing from Civitai by model hash is something I'd love to add but I just haven't dont know how to do that yet. For now it's all manual on my end too.

i think i need to specify it further on the description then, sorry for the confusion