Again, don't want to second-guess the guys on the ground. But I've read the book as well and Luttrell does not at all make clear that the SEALs know for sure the Afghans (including a 14-year-old boy) were Taliban supporters. He only reports that the Afghans were not friendly to the SEALs, to which I would ask you - would you be friendly to a bunch of heavily armed foreigners who appeared on your land pointing weapons at you?

The book also points out that killing the Afghans would hardly assist that much in avoiding discovery, as the Afghans were accompanied by their flock of livestock who would certainly wander all over the place without herders and be instantly conspicuous, as well as instigate a search by the villagers for their missing men. Strangely the SEALs were not carrying zipties or 550 cord to simply detain the herders, which would have had roughly the same value as killing them as far as concealment was concerned.

IIRC, the SEALs did not attempt to continue w/the mission, since it was blown anyway, but tried to evac and establish comms. The Taliban ran them to ground before they could do so.