1.No way you thought this was simply after blue hole with Garp all bruised up, bleeding, clothes ripped/jacket off. This was after god knows how long of offpanel fighting.
2.This the very next page after the panel you posted
Garp is already showing clear signs of keeping Kuzan and BB pirates busy so that sword could escape.
3.
Garp has this mentality, the minute he left for Hachinosu he would have already considered the very real possibility of sacrificing himself. It's just that if Kuzan and Teach weren't around, he wouldn't need to. Once he saw Kuzan was on the island, Garp ain't stupid like I said, he probably understood the chances of letting everyone escape while also escaping himself have now been reduced considerably, the dude can freeze the ocean in the blink of an eye, Garp at bare minimum would have to keep him busy long enough for them to escape, he doesn't think so little of Kuzan thinking one blue hole could do the job 💀, he was probably hoping he would pull a Kizaru and stay down on purpose if anything, but the cards were in Kuzan's hands and Garp knows that.