What should I do if I receive unknown email suggestions?

I was filling out a survey and the email suggestion that Apple gave me included a mail from someone I do not know and have never contacted either. I checked and the only emails I’ve got in my account are mine (in Icloud, messages, email…), this email was not in my contacts nor was it on the website. After opening the survey once more, now the keyboard only suggests *my* email account, whereas before it suggested both. Does anyone know if this is a security issue or just some sort of bug?

[Re-Titled by Moderator]