At 1:39 in Duplication Objects, Grant instructs us to “tab into Edit Mode and then G to grab in the Zed”. How did he select the top faces of the crenellations? I had to go to Face Mode and then click on each face separately. Am I missing something?
It is effectively the result of his last action on that wall section having been extruding up the crenelations. Blender remembers what was last selected in edit mode. (It was back in lecture Castle walls.)
But yes if they are not still selected you do just select each of the three faces by clicking on them, then you can G Z to move them.