Genitive describes the syntactic case produced by a governing element; its visible sign is not always kasra.
بِعِمْرَانَ: genitive, marked by fatḥa because it is a diptote.
بِسَعْدَانٍ: genitive, marked by kasra and tanwīn because it is fully declinable.
Distinguishing case from case marking is essential to correct parsing.