Yeah Netflix accounts are a big target for hackers, the chances are the credentials you use to login on Netflix have been stolen previously and released online. Typically hackers try known usernames and passwords from other sites on Netflix in the hope of gaining access, and because many people recycle passwords this is quite effective.
A good tip is to register for haveibeenpwned.com which will identify if your email address has any security issues.
Its always advisable to use a different password on each website, preferably with two factor authentication. Apps like 1Password can make this easy to manage.
