Swiping his sword at the granny who had her hand heading for Malachi's throat, Leo watched as she jumped a very far distance away from him.
From afar, when he had been wondering where Malachi had gone and was waiting for him, he had caught sight of what was happening here and rushed as fast as he could.
However, Leo didn't really mean to cut the granny's hand away from her wrist when he swung at her. His plan had just been to place the sword between her and Malachi to warn her.
From afar, Leo had been wondering why Malachi was not moving as someone slowly made their way to his throat when he saw the red irises of the granny. Immediately, he knew that she was just like his daughter and had powers.
In less than a second, Leo concluded that Malachi and the granny had something going on between them, and the granny had used her power to do something to him.