And it is possible that Kawaki used the absorbed ninjutsu from Garou against Garou. In my opinion, Kawaki is able to absorb ninjutsu and store it in his seal and then use it in any manner that fits him. Also, one might say that why wasn’t Kawaki affected by this huge blast?
Well, we did see Garou pierce his chest without any effect and I think that here his modified internal organs play a huge role. I think that Kawaki’s body is capable of healing itself with ease and this is possible only because of his advanced modified internal organs. We know this for certain, that Kawaki is a modified human being. Katasuke observed excellently that Kawaki passed out due to his body overheating. Indicating that Kawaki is still a work in progress.