Yup that is correct! Read the email carefully, it may just tell you we're going to renew the domain, not that we're going to charge you for doing it!
If it does look like we're going to charge you, contact email@example.com and have them check to make sure it's correctly tied to your hosting account and therefore free.
We send renewal reminders every time we're going to renew a domain because frequently people don't want them anymore (even if they're free!).