you are correct in general but not in this case. his given name is simply Mohammad, just that. that's what he is called by friends, family etc. Seyed is just a title. (everybody else in his family has that too) he just wanted to be cute by writing that on back of his shirt.
unfortunately this is a new trend in most of Iran national teams in different sports, players just write whatever they want on back of their shirt, you can find everything in just one team. surname, given name, sometimes just a funny nickname to look cute