It's a bit strange to call an app "Abandoned" because the last update was 6 months ago. When an app is mature and stable, it doesn't require a steady flow of updates to be good and useful (except as a way for developers to show that they are still active and "please" their users).
I'd call it abandoned if it didn't fit the platform standards, if it was buggy, if it didn't run on some new devices…
If you go to the istore version history for the same app, there have been regular feature updates and bug fixes in the same time frame. Are you implying that the android version simply doesn't have any bugs to fix?
This update in September is enlightening:
Added support for iOS 11 password autofill.
You know which other OS introduced system-wide autofill suppport? Android Oreo.
I think it's safe to say that Instapaper is abandoned on Android.
I'd call it abandoned if it didn't fit the platform standards, if it was buggy, if it didn't run on some new devices…