Lesson error? Ruy Lopez - 3...Nf6

ok so why do u think there is an error?

White to move and win.

This is a famous game, composed by Lasker in 1894.

Moreover, if u want us to check this lesson, why not giving a link?

The error was Black’s in allowing White to reach a position to carry out Anastasia’s Mate.

It is a lesson which shows what happens if black plays carelessly : that is the whole idea to show the "mistake(s)".

Bien entendu

6.dxe5 happens on a line given with 5.d4.

No need to be a genius for stating it.

The comments are a bit outdated, as mentioned, i.e 5Re1 played three times in last WC Match between Carlsen and Karjakin. You could get clue of good ways of playing against 5Re1 from those games.