I believe Shinichi’s weird habit is that he uses glissando, where you “slide” from one musical note to the next. This is heard going from the last of the three “faster” notes (the G in the B A G triplets, labeled below in brackets) to the following “landing” note (B half note): D -> G -> G -> [B -> A -> G] -> B
If you listen carefully to Reiko’s version of Amazing Grace and the flute+piano version, you’ll find that there’s no “sliding” between the G and B notes; you hear each of those two notes clearly, like in steps.
*String players and/or others knowledgeable in music theory, please correct me if the actual term should be “portamento” instead of “glissando”. I tried looking up the difference between the two but I’m not entirely sure which the appropriate term would be, particularly for violins.
-that's what Shinichi-niisan would have said....