He swept air, which told him that she had jumped, but when he heard one leg come down instead of two, he knew that she was countering again. And more importantly, he realized his position was compromised. It was no surprise then that when he brought his hands together to intercept her ankle and her kick how close she was. When he attempted to grab, his intention was to twist her around by the leg to turn this into a grappling match.
Which was usually what it turned into, but especially in this instance he wanted her close. Because the absolute last thing he wanted was to give her a black eye with a stray punch or kick that got through. He would not insult her by holding back, but at the same time he did not want to make any real visible or lasting injury on her. Especially given the way that his students adored her.