This app was mentioned in 1 comment, with an average of 5.00 upvotes
They have a separate app which is the demo: https://play.google.com/store/apps/details?id=org.ovh.grzegorzaeSTG2
My guess is that the full app is on sale for free and they meant to change the description to indicate this. But someone screwed up and just copied the description from the demo. But I could be wrong.