No, it is not an error.

u1 is deleted. Cost 1 u2 is substituted with v3. Cost 0 (Equal labeling). This Operation together with the first Node deletion implies the deletion of edge (u1, u2). Cost 1. u3 is substituted with v2. Cost 1. This implies the substitution of edge (u2,u3) with (v3,v2) with cost 0. u4 is substituted with v1. Cost 0. This implies the substitution of edge (u3,u4) with (v2,v1) with cost 0 and the deletion of edge (u1,u4) with cost 1.

Hence, we have a total cost of 4.

No, it is not an error.

u1 is deleted. Cost 1.
u2 is substituted with v3. Cost 0 (Equal labeling).
This Operation together with the first Node deletion implies the deletion of edge (u1, u2). Cost 1. 
u3 is substituted with v2. Cost 1.
This implies the substitution of edge (u2,u3) with (v3,v2) with cost 0. 
u4 is substituted with v1. Cost 0.
This implies the substitution of edge (u3,u4) with (v2,v1) with cost 0 and the deletion of edge (u1,u4) with cost 1.

Hence, we have a total cost of 4.