This move order is a common transpositional tool for Scheveningen players to avoid the Keres Attack, which is reached from 6.g4 from a standard Scheveningen position. While it initially follows the Najdorf move order, the e6 push is more characteristic of the Scheveningen than the Najdorf, where black often plays a direct e7-e5 push.
Note that here, white can choose to follow up with 7. g4, but this line is referred to as the Perenyi Attack rather than the Keres Attack. This is because now that a6 controls the b5 square, black can play 7...e5 without fear of 8.Bb5+. Normally, in the Keres Attack, that would result in a trade of light squared bishops. But in this case, black now has two attackers on the exposed g4 pawn, where there is only one defender, the white queen. Further, 7...e5 threatens the d4 knight, so simply moving 8.h3 to protect the g pawn drops the knight. White's move, therefore, in the mainline Perenyi Attack, is 8.Nf5, cutting off the bishop's assault on g4 while moving the knight to temporary safety.