It's unclear how the wish granting system works in the movie, but whatever you wish for somehow manifests but not exactly the ways you might have imagined for.
Barbara wishes to be strong like Diana so she gets strength like Diana but not the other qualities.
Emir wishes for his inheritance to be recognized, so a tall wall comes up.
How do you explain all that ? We can say it's element of magic which is unexplained.
Similarly Diana wishes for Steve to come back, well maybe if she had specifically asked for Steve in his body the story would had been different. But she only asked for Steve, so my guess is the spell working behind the wish-system brought back Steve's set of memories from some cosmic database of memory.
As Steve was dead years ago bringing his body might be difficult for spell-system unless it was preserved in some ice ( like Captain America ).
Steve's memory possessed the body of a random stranger. But Diana chooses to see only Steve in that body and hence the face of Chris Pine.