is one piece episode 738 filler?

Two years ago, a 20-year-old Sabo sat atop the mast of a ship, when he suddenly saw faint outlines of Monkey D. Luffy and Portgas D.

Ace as children standing with their backs to him, though due to his amnesia he could not tell who they were. Luffy and Ace said Sabo's name and turned to face him, but Sabo was snapped out of his vision by Koala, who was excited that they would be returning to Baltigo for the first time in a month.