Why is Email Opt-in appearing on two different pages, when I only added it to one?

I clearly haven’t got to grips with using Pages because I have an issue I can’t fathom here.

I created a Join our club page then edited it in the Online store customiser, adding an email optin to the bottom

https://anyoldvintage.com/pages/join-our-club

Nice. But then I look at my About us page - and the email optin has appeared at the bottom of that page as well!

https://anyoldvintage.com/pages/about

Can someone explain this to me please? There must be a template issue here that I don’t understand.

Thanks!