There is a prehistory to bouzouki music, that we really don’t know much about. The conventional narrative is that the music came to Greece with refugees from Turkey in the 1920s. But we know that bouzouki-like instruments were being played in Greece throughout the 19th century (the tambouras specifically), and this picture is only one of the more lusty portrayals of it.
What we don’t know is what music they were playing. Greek scholars were slow to transcribe music, and were picky about what they chose to transcribe.
Given what we know about Muslim Cretan music (currently being revived, and which also featured bouzouki-like instruments), I don’t think it’s too hard to work out why no one transcribed those 19th century songs played on instruments that looked like bouzoukis. The reaction of scholars in the 19th century would have been just as dismissive as that of scholars in the early 20th century. “That music isn’t Greek, it’s Turkish.”
Never mind that a disproportionate number of fighters in the Greek war of independence were pictured playing it. (And in the case of Makriyannis, wrote about it.)