Board Thread:Wiki Discussions/@comment-3422208-20140626180208/@comment-28861328-20140626183455

Elveonora wrote: How do you think it copies techniques? It memorizes them and also we were shown Sharingan replaying things not once. Itachi showed Sasuke the Shisui flashback, remember?

That was done through genjutsu to show Sasuke the memories of Itachi. Different thing here. Black Zetsu is specifically noted to record entire events.