This is exceptional musicianship. What I saw (the last blues scale video) can be a real eyeopener if you want to play jazz. Not easy stuff though! And not suitable for one row players.

Do=C Re=D Mi=E Fa=F Sol=G La=A Si=B and that brings us back to Do. Dièze means sharp. Fa dièze = F#.
The blues scale is a scale in B minor (Si mineur), on a C/G accordion, played mainly pulling (en tirant).
If you know this, you can play along with the blues scale.

The B minor explains what's going on. Thanks.

For their videos that are not the blues scale, seems like they are using a synthetic scale, which is likely what gives French accordion music its distinct sound, but probably largely inapplicable to cajun/zydeco.