What do you consider primary sources in this context?  She notes the obvious homoerotic passages in Rydberg's poetry and fiction, which are primary sources for literary criticism.  The details of Rydberg's sexually troubled childhood and his uneasy relationship with women were presumably taken from his standard biographical sources.  I have no idea what sources Svanberg and Stolpe used; I can't ask them.  Again, no other scholar has questioned the accuracy of their conclusions, which seems to me to be the definition of a scholarly consensus.