Can yahoomail auto log in to an account that has never used my computer?

Is it possible for yahoomail to auto log in (on my laptop) to an account that has never been used on my laptop? I was traveling internationally and, therefore, bouncing between many wifi networks in different countries, including crowded airport/plane networks. When I arrived home, I went to yahoomail and it automatically logged in to a complete stranger’s account. Does this make sense? My thinking is that somehow, between all those shared wifi connections, someone’s log in got “into” my computer. As may be evident, I’m not too tech savvy and I’m very curious about this. If it matters, I use a Macbook and Safari. Thanks.