Answer: You marked to follow them. Doesn't matter if you are friends or not, anyone you follow will be showing on top of all feed, reviews and tips.
It's good to follow someone on Yelp. It's completely anonymous until November 28, 2017. After that, any new follower will be visible (updated per Yelp Blog 11/02/17). They don't know you are following them. Befriend with someone on Yelp will reveal each other's check-in messages. I don't see any harm to follow your friends. Except, the contents from people you follow will go to the top of everything.
|I like extremes. Porsche posted over 17k media.|
From what I know besides reviews, tips, photo post notifications, you'll receive notifications from your friends' interests in Events and posts on Talks on the feed. It's much easier to read them on the app because they presented in both groups, Friends and Following.