The Pages versions compatible with High Sierra are v7.3 thru v8.1. Apple does not provide past full installers for direct user download.
When you launch the Mac App Store, you should sign in with the same Apple ID as you used to install Pages previously. Then press the option key while selecting the Mac App Store's Purchases tab. When you click on the Pages entry on the purchased panel, it will present the first dialog that you offered above. If you click Download, it may offer a second dialog asking if it is okay to install the last compatible version of Pages for High Sierra. If that dialog appears, do the obvious.
It is unclear to me if the Mac App Store will volunteer to install the last compatible version of Pages if you currently have v7.2 or earlier installed, which are not compatible with High Sierra.
There is a Pages for Mac Support Community for these types of product posts.