TB54 natively the Flarum post composer shows the raw post content, which include showing the raw emoji Unicode character instead of an image. So the look of the emoji in the composer will depend on your operating system. Only the picker and preview use a common "forced" image across all platforms.
That's how the Flarum native emoji extension works, that's how my emoji picker extension works and I assume it's also how this extension works (I haven't used it though).
As far as I know, only the "WYSIWYG / Rich Text Editor" extension adds WYSIWYG-like behavior to the post composer. All other extensions rely on Flarum's default text editor which will always use the operating system to display special characters like emojis.
