Maybe becuz they are one in the same,I think as he was being crushed his S/T jutsu was awakened some how and if you read the latest chapter then you know that part of the body prolli went to the other dimention...This is all speculation btw so it may be tru or noti wonder how or why tobi knew a kid who just barely opened a two tomoe sharingan knew he was going to have a convenient space/time jutsu