I think its because at the time of the photo the sister was young so maybe he wanted to have a photo of his young self too, thats why she said Yohan "always wanted to be the center of attention" he could've been saying I was cuter at her age or something like that.
If i remember well from the novel they said that yohan was the one who took the picture (bc he likes being the center of attention so he does things like that) so its a mirror not another picture edited
Ohh got it!!
Why is Yohan still in a different frame in the family picture??