really..... a tiny, 8mp sensor is basically the same as 8mm film...
It's a pretty darned good sensor. 8mm film delivers the equivalent of 700 lines resolution, so a 720p or 1080p can match it. Color depth is pretty good too. 8mm film
might be better, but both are close enough that most viewers would not notice the difference short of a side-by-side comparison focusing on quality differences.
It's not so much the resolution & color depth at issue, it's the "feel" characteristic of typical 8mm systems (camera, film, processing, editing, transfer...), the little color degradations and scratches and jumps, which viewers will be far more sensitive to. Seems this app recreates that feel well enough that a transition between film and digital will go unnoticed by most of the audience.
I'm sure the director could discern the difference. I'm sure he also knows whether his audience would. A subtle shift in visuals is far less an issue than not getting shots critical to completing the movie.