Storybook doesn't serve fingerprinted assets

I’m running this storybook demo locally.

I ran mix phx.digest to generate the fingerprinted assets and the cache_manifest.json file under priv/static.

I expected that if I run MIX_ENV=prod iex -S mix phx.server, the fingerprinted versions would be served, as specified by the cache manifest file, e.g.

{"assets/app.css":"assets/app-f8a5443d8c07b13b93aea499ce32f517.css"}

But that’s not the case. The same happens in the online demo.

Is that expected? How can I serve fingerprinted assets with storybook?