The app is not showing posts that don't contain a picture, but shows posts that do. So if you browse someone Mastodon account on Pixelfed, you will see just fraction of their posts.

https://ploum.net/2025-12-04-pixelfed-against-fediverse.html

I don't think it's important at all because nobody really uses Mastodon anyway; but it shows that doing decentralised software is hard, because each actor can just do whatever they want.