It's virtually impossible to authenticate to a random account, as it requires both the username and a password. Even if you typed in a random email, typing in a random password would have to randomly be the same password for the random email, which has astronomical odds. If it did so automatically, the account it signed into was one stored in your browser cookies at the time. If you're on a public PC, this might be an issue, because you'll need to find whoever used the computer and logged into their Microsoft account from it. If this is your personal device, then you should be able to easily find who you let use it. To unlink the wrong account and then link the correct one, you can go to your Bungie.net Settings, then to Accounts & Linking. There, you can unlink and link accounts.