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.
I would be in favor to switching to a custom curated list of emojis when no keyword is entered. If we expose that list through an extendable javascript method or forum attribute this would even give an easy opportunity for extensions to change it if needed.
