添削前/Before Correction
-The library has a myriad genres of books.
-Considering the way he said it, the comment seems tongue-in-cheek.
添削後/After Correction
-The library has books in a myriad of genres.
（その図書館には無数のジャンルの本がある。）
-Considering the way he said it, the comment seemed tongue-in-cheek,
（言い方から察するに、彼のコメントは冗談半分だった。）
他の表現/Alternatives
The comment seems tongue-in-cheek, at least judging by the way he said it.