In my opinion this makes sense? To react with an emoji, it requires more interaction from the user (tap and hold instead of a simple tap), which you could make

In my opinion this makes sense? To react with an emoji, it requires more interaction from the user (tap and hold instead of a simple tap), which you could make an assumption that it signals it received more of the user's attention and is more attention-worthy content. This can be both bad and good, but is not inherently bad in itself. I can see why some would argue that an angry emoji could lead to a more negative news feed, but five out of the seven emojis you can react with are "positive", so you could also argue that positive content would drown out the negative content (assuming that there's an even distribution of interactions between emojis). At the end of the day, this was part of a study to understand human behavior, and without the study they would have no understanding of how emoji reactions could be used to improve a user's feed and improve their platform.