How would you explain this sentence?
My first few months inside, I spent a lot of time trying to piece the war into a pattern. I developed the habit of making a mark on my cell wall when I remembered a particular event, thinking that at some later date I could refer to it and assemble all the marks into a story that made sense. I still remembered what some of them meant for a long time afterward: that long chalky scratch below the mirror next to “FTA” stood for that kid whose head Murph cradled in the orchard as he died. The one above my bunk reflected an instant of thought I’d had in an alley in Al Tafar, in the heat of that first summer when the shade of webs of power lines were little blessings as we passed beneath them, and a corner was turned by whoever had been on point that day, and I saw Sterling as he turned around and waved for me and Murph to cross into the open road, and it occurred to me that Murph had had a choice, there were two paths he could have taken and I was one of them, and--------and I asked myself if I could be worthy of that task, and wondered if that is what his mother meant when she asked me to take care of him, and is that why she asked?
How would you explain this sentence: wondered if that is what his mother meant when she asked me to take care of him, and is that why she asked? What does “that” refer to?