This is likely a recognition of a hit and ignorance of misses. If the friend was suggested before then you probably wouldn't notice. But there's still a lot here that even me with little information can give reason to suggest that friend. For one, you mention that it was an old mutual friend. Facebook is going to use the metadata (you talking to your friend) and search for potential mutual connections. But there's more. If that friend recently talked with that other friend (likely a prompt for that discussion), Facebook knows (either by GPS or by mutual conversation on one of their platforms, or even a friend of that friend connection).
I'm not trying to say that Facebook isn't reading your messages (I doubt they do tbh, because ->) but rather trying to demonstrate that they don't need to in order to make these creepy connections. This is the importance of metadata. Data you may not even know about!
Think about it this way: a private investigator sees who you talk with, how long, where you go, etc. But they don't have the actual record of your conversations. The PI is working on metadata. We find this creepy and invasive because we can recognize how this information can be used to gather intimate aspects of our lives. Companies like Facebook are essentially doing the same thing but at scale. And you can probably imagine how the scale both helps and hinders this invasion (but likely overall helps).
Just someone we played sports with. He didn't live in our city, moved away in his youth, and we had zero friends in common on facebook. Haven't seen him suggested as a friend since he disappeared as a suggestion a couple of weeks after that.
I think you've missed the important information I was trying to convey. What sparked the conversation about that friend? Did your other friend say "Hey, I ran into so and so recently"? If so, then that's more than enough information for FB to make that connection (FB sees that these two people were in close proximity, through GPS, and stayed near one another for an extended period of time. Meaning they probably were talking). But that's not the possible path to the suggestion.
There is also the psychological aspect of we recognizing hits more than misses (in this case. Often it is the reverse but context matters).
I'm not trying to say that Facebook isn't reading your messages (I doubt they do tbh, because ->) but rather trying to demonstrate that they don't need to in order to make these creepy connections. This is the importance of metadata. Data you may not even know about!
Think about it this way: a private investigator sees who you talk with, how long, where you go, etc. But they don't have the actual record of your conversations. The PI is working on metadata. We find this creepy and invasive because we can recognize how this information can be used to gather intimate aspects of our lives. Companies like Facebook are essentially doing the same thing but at scale. And you can probably imagine how the scale both helps and hinders this invasion (but likely overall helps).