Complex sentence: This resulted in the anomaly of a river with masculine gender: all other Rigvedic rivers are female, not just grammatically, being imagined as goddesses and compared to cows and mares yielding milk and butter.
Split into simpler sentences: This resulted in the anomaly of a river with masculine gender: all other Rigvedic rivers are female. This is not just a grammatical designation: the other rivers were imagined as goddesses and compared to cows and mares yielding milk and butter.