Yea its best to pot straight into your main Container, Or you can plant in a solo cup and 2-3 weeks in when its nice and rooted, transplant it. But if his plant is only 1 month old and its stunted like that? Idk if its pot size. because the same exact thing happened to me when planted straight into my 3 gallon pot. It could be his soil perhaps or like i said above, faulty seed which has happened to people quite a bit