I mean, sure you can misconstrue it as being relevant to the plot of the series. This book is all about Shallan and how she finds this awesome book. And if you know anything about Shallan from the first book, she's hardcore into books and knowledge and such. Also Radiance has to do with the Knights Radiant. So it would kind of stand to reason that Shallan finds a book about the Knights Radiant. But no, his title is clearly a comment on how big of an ego he has.