What does Prabhupada mean when he refers to Drona’s leniency?

From: Apurva Pradhan

BG 1.3 : In the purport, Srila Prabhupada says “By this he wanted to point out also that she should not be SIMILARLY lenient in battle..”. Is this SIMILARLY is referring to Drona training Dhrishtadyumna? If yes, wasn’t Drona just performing his Dharma (to impart training to anyone who approaches him) which cannot be considered leniency. Kindly help.