The article says to use the "XOR of all elements" method to find u^v, then do the partitioning, then use the "XOR of all elements" method on the first partition to find u, then use the "XOR of all elements" method on the second partition to find v.

tromp is saying the last step can be simplified. There is no need to use the "XOR of all elements" method on the second partition to find v, since the earlier steps have given us u^v and u, so simply XORing those two values together gives v.