If you look at what is listed it kind of tells you. Phone Idle, means the minimum power it takes to keep the phone "on". Cell Standby is the power it takes to stay connected to the phone network. (not even sure that including data services, as LTE would chew through the battery a lot faster) Since screen uses the most, but doesn't use that much more than phone idle and cell standby and you see that messaging it taking up quite a large percentage also.
Basically, he only used his phone for occasional texting over the two days. I say occasional as if he were doing it all day, the screen would have eaten much more of the battery than idle and cell.