his intentions was obvisely to kamui his whole body but he didn' mastered it vs deidara it was the first time he used it.an arm is pretty good for a first attempt on a flying target who isurm... have you seen kamui suck up a full body? no... when it was used on a full body it took a arm only... absence of evidence isnt the evidence of absence
-akatsuki member
-escaping while flying
-far from kakashi
-got same speed of kakuzu 4.5 in databook
it would be beter for him to says
"i don't know if kakashi is able to kamui an entire body" than affirm that he can't since it's never stated clearly.