The journey Kishi brought up was the one he had right after he tapped her forehead and told her he will be back, seeing Sarada in 700 clearly indicated that he came back right after the end of the events of The Last judging from her age compared to Boruto.1. Ask Kishimoto? I didn't make that up.
2. Sasuke is way too strong to be doing reckless missions for no reason. He is probably on his journey searching for what I explained before. I mean why else would Kishimoto bring it up?
Radon is right, he was probably on a mission, or he was looking for something, but there is no way he was away for 10 years, Sarada misses her "papa" which means he is busy but comes home regularly.