Usually in comparable generative programs if you set root note/scale the programs I know only generate songs that are completly follow that scale as MAIN rule for evrything after (melody, chord progression.....). So the resulting song will ALWAYS be in G lydian no matter which other settings you choose.
I have to say I am really not good in music theory (thats why I use these kind of tools :-) ) but it seems that in your tool setting the root note/scale is only ONE component for song generation and you have to exactly know which chords you have to use to get a song in G lydian finally and not in G major.
I really would prefer to work it in the way the other tools do so if I set it to G lydian the resulting songs will be in G lydian, maybe that could be done on the road of further devellopment ? At least as an option to choose.