This change happened in Flarum release 1.3.0 when we updated
simple-emoji-map library from 0.4 to 0.5 which added new emojis to the list including at the very beginning of the list. The emoji picker doesn't have special logic, it always shows the emojis in the original order from the list filtered by the keyword. When no keyword is entered it just results in the beginning of the full list being shown. It just so happened it started with the faces category and the first few of that category happened to be commonly used emojis. Though I remember that selection also contained a few very similar emojis because of that fact.