In this video, the accordion right hand is a simple external mic stand holding on to a dynamic mic. On the left hand there seems that there is a smaller dynamic mic taped or inserted to the accordion. Percussion mic would be a good guess, as it seems to be a lot smaller and looks to be taped to the opening. Percussion mics are great for capturing loud drums, but far from good compared to even a standard mics in terms of dynamics and sound capturing quality.
These mics are not the best for sound quality, but acceptable for stage/live performances where lower price, strength, reliability and ease of replacement are why people use dynamic mics in these scenarios. One could probably use something like Sure SM58s at around $100US new a piece and get pretty much the same results.
I would prefer small mics in greater number under the accordion covers or inside the accordion itself where sound quality captured is the best for live performances. Feedback and sound contamination is also greatly reduced. Coincidentally, since the accordionist is using a Pigini accordion, Pigini has the services of Heinz Aumüller, a fabricator of high end (both price and quality)
accordion mic systems through Excelsior/Pigini. The perfect solution for someone performing like this.
For studio recording, lots of options are out there, however, the better ones involve either small or large condenser mics of professional quality.
but this video offers tantalizing glimpses:
