The pmap output he shows near the end has Address Kbytes RSS Dirty Mode Mapping 0000000000400000 2460 832 0 r-x-- pdftex

The pmap output he shows near the end has Address Kbytes RSS Dirty Mode Mapping 0000000000400000 2460 832 0 r-x-- pdftex 0000000000400000 0 0 0 r-x-- pdftex 0000000000867000 8 8 4 r---- pdftex which means the core pdftex binary does not have PIE (sadly a very common occurrence on Linux). pdftex handles certain TeX functions that invoke external commands, so it has calls to system().