This seems to go further than just instruments. Years ago, an Irish anthropologist did studies and concluded that a fair dergree of early Irish music was structurally similar to Indian music. He stated you could hum a number of different Irish folk tunes to certain Indian populations and the Indians could finish it! One thing for sure, The Celts sure got around. The civilizations of Galatia (Turkey) , Gaul (France) and Galicia (spain) all contain the root “Gal” or “Gael” and indicate Celtic settlement at one tme.
CC
And, the Celts crossed out of Central Asiia, a lot longer ago than this.
No one captured the melding of civilizations better than Kipling.
Makes sense to me.
I play in a Celtic group, lived in Ireland as a kid, etc.. I found playing my fretless bass along with ragas to be pretty natural. The western 12 notes to the octave is merely a convention, not an absolute.