Other than it being a traditional toy that every japanese should know of (that's why Shouji was like "lol this kid doesn't even know kendama), i don't think there's any particular significance....
It's this toys name. http://www.mangago.me/read-manga/hakuyou_ayakashi_gatari/sa/sa-c002/5/
Oh, that's kendama. Learn something new everyday, and now the comment makes total sense. Thanks!
Thanks for linking the picture. Now the comment makes total sense. Also, Shouji has a real project on his hands — not that it looks beyond him.
Ur welcome :)
Early Christmas present, thank you!
(Is there some significance to kendama? What is that?)