Yeah, that's not the app store icon, it's the generic Apple icon for an application. I would leave it, it indicates a Mac app, but not a MAS app.

I think when coupled like this, "[logo] buy" it gives the impression of "something apple".

Personally I thought that it would either open the app store, or that is was something related to Apple pay (although that one needs "[logo] Pay").

It felt a bit misleading.

I think you are talking about the top right not the button?

Oh, yeah that's right.

Nah man, you got a nice looking button there. I'd stick with it unless you get a warning from Apple. Keep up the good work!

That icon means 'app' not app store.

The logo he's using is not the AppStore logo. It's the logo for a generic app with no custom icon on macOS. That said, apple still own that logo, and might have an issue with it.

It's literally the app store logo minus the circle. But you're right, the same icon is also used as part of the generic app placeholder icon. In either case, it does still belong to Apple.

Edit: In fact, thinking about it some more, it's very clearly much closer to the App Store logo than anything else. It's literally the white silhouette design from the logo (as opposed to the colored non-sillhouete version from generic app icons), placed on a blue button that's similar to the app store logo's blue background.

The app store button is the one with the app icon and saying available in the app store.

The folder on my mac uses that icon for Applications.