A while ago someone I stayed in touch with over 10 years ago appeared in my suggested friends list. That was probably due to a mutual friend. I looked at the suggested friend's page and public posts for a bit, and decided to not send a friend request. Later that day I was told that he accepted my friend request.
I don't think I made a mistake and accidentally sent a friend request. Furthermore, in the friends activity log at https://www.facebook.com/dreamlayers/allactivity?privacy_source=activity_log&log_filter=cluster_8 I see a "became friends" entry, but no "sent a friend request" entry. I just scrolled through the entire log, to the beginning of my time on Facebook, and still see no friend request. For various other people I see a "sent a friend request" entry followed by "became friends".
This isn't a problem and what happened was probably a good thing. So, I'm not complaining. It's just weird and I'm wondering why this happened.