Based on the source code, it doesn't look like the extension is loading any additional discussion, it's using what has already been loaded. I'm not sure what the UI looks like, but based on the code it looks like if you load an additional page in the discussion list, then the additional discussions will be used for discussion cards if your count setting is higher than the default page size of 20 (that's Flarum page size).
If an extension hits the API, they can request up to 50 discussions at the same time. For more they will need to modify the global limit or add a custom API endpoint. But it doesn't look like this extension is doing any of that.
If you find an extension that changes the Flarum page size, it should also impact that extension. But I don't think anyone created an extension that lets you change that. There are some challenges because Flarum requires the page size to be modified in multiple places and not all can be extended in the proper, least-likely-to-break-updates way. There might be a setting for default page size in a future Flarum version once we fix this downside. But regardless, if an extension has a setting for number of discussions, it should either validate the value with an upper limit or actually implement it in a way that will work regardless of the Flarum page size / preload size.
