He would half to be left-handed to write the + sign like from that angle on top. Southpawanon here.
Have you ever seen some lefthanded people write the number 4? They start at the bottom go up and around, if that plus was written at the top left side of the page that is how you can tell it was done by a left handed person, otherwise the proper place it was written by a right handed person would be on the bottom right.
When I right (being a southpaw myself) I always start on the left side either top or bottom. And just for posterity I do everything opposite that right handed people. My clothes hanging in the closet has been an issue with my ex. He used to put his clothes in teh closet with the front of them facing to the left, I put mine facing to the right.