Sentence 1: Pa was in th' Rangers, an' he had this run-in with some Comanches "Anse's eyes were suddenly bleak, and Drew remembered the few stark sentences the Texan had once spoken to explain his reason for being in the army a return to a frontier ranch to find nothing left, nothing he wanted to remember, after the Comanches had swept across the countryside.

Sentence 2: Drew was remembering what the Texan had said for his reasons to be in the army.
Is this second sentence entailed by the first sentence?
yes