I was chatting to someone one afternoon who I didn’t know before, didn’t already have her number and didn’t swap phone numbers or anything.
That evening, without having looked for her on Facebook, she’d popped up as a Friend Suggestion (not a Friend Request by her, a FB suggestion).
Then a few weeks later I saw her Son (who I already knew) to say hello to and she popped up again as a Friend Suggestion by Facebook that evening.
It’s one of the reasons I came off Facebook. I didn’t even have a profile on it until about two years ago and only stayed on it for a year. I think it’s a very strange thing, it may be the years of drugs playing with my paranoia but I kept thinking that the Facebook app could listen to me or could even watch me.
Did you have mutual friends before meeting each other? Location data (GPS, WiFi etc) plus you being mutual friends and you being physically close to each other that day may well have been enough for FB to put them as a suggestion.