Dont confuse "original" game with "totally new idea".

He basically combined a classic WW1 Airplane shooter with
"sky city" and "old time cinematic" effects.

Its not that he invented something totally new,
just sombined them in an original way.

The lesson is more another thing which is a best practise for indies:

Use an Artstyle wich looks original but requires little
development time compared to the big titles.
So using a stylistic artstyle, color palette, objects with
low detail graphics, works great for indy games,
as creating the assets requires much less time
to actually get is all done.