Toph still “sees” Korra as Aang.
Everyone Korra has met from the old Gaang calls her by her name or “Avatar Korra” but not Toph. Korra’s footsteps aren’t like Aangs and I don’t think Toph heard Korra’s voice before this encounter (well at least not her 10 year old and up voice) so how would she recognize Korra? By her spiritual presence.
I feel that Toph and Aang were so close and their spiritual connection is so strong that since Toph can’t “see” who the next Avatar is, she feels Aang’s presence and Aang’s spirit instead.
"Some friendships are so strong, they can even transcend lifetimes."