The app takes the hgt files from the servers of the developer (not configurable) and places them into the oryxmaps default DEM directory (can be changed, external sd card for example).
The files are SRTM1. I don't know the source of the data, but surely it would be worth a try to contact enemotrop. If the LIDAR based data sunny uses are so much better, then he could use them as source instead...?