Somebody knew my real name in a game

So I was enjoying a game of aram when somebody on the enemy team suddenly talked to me and said my first name. The game then finished and he left the lobby without another word. I havent used this username anywhere else except for league, not on skype, discord or teamspeak. Also i mainly play solo on this account The mailadress for this account includes my first name but not my last name, hence I think he somehow found out my mailadress. How could this be possible? Has there been a leak in riot's database? This is kind of creeping me out, knowing that someone could have access to my personal data Thanks for responding in advance!
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