In the anime, a young Luffy blurted out that the trio shared a promise over a shared drink. Garp overheard them boasting of their dreams to become pirates, leaving him infuriated. Garp then chases them out into the night, breaking down trees and rocks and beating them all to a pulp.
Sabo exclaimed he was a monster. Afterwards, he casually leaves them, saying that he will not be so merciful next time. This was not shown in the manga. In the manga version, Garp was shown saying hello first before “training” them.