why do you care if i know this person and who are you?

i rung up this guy in his 40-50s and he asked if i knew this girl and i said i did and he was like "i figured as much and left" who the hell just randomly assumes i know someone. he didnt even explain who he was and when i asked the person who he asked about they had no idea who they were and was creeped out. someone has a stalker