Question how unique that nickname actually was. Plenty of common ones out there like buddy or champ. Could have just been a lucky guess. Brains also look for patterns where there aren't any. Might be reading way too much into a random moment.
Recall my friend Jake getting called 'Red' by a cashier, a name he hadn't heard since grade school. He swore it was a glitch, but then we figured the cashier might have just seen his old keychain (it had 'Red' on it from a baseball team). Kinda makes you think @henry_martin37 has a point about our brains finding patterns where there aren't any.