Taking out a would-be suicide bomber caused a predictable secondary explosion, which is what killed members of that family. Once the context conducive to such bombings came into being, avoiding innocent casualties while taking out would-be suicide bombers may not have been possible. IOW, LIEden's failure was in not securing access to Kabul airport along with shutting down Bagram, making Kabul airport the sole means of exit.
LIEden painted himself into a corner, leaving no good choice within his range of choices.