There is this impression people seem to have that Greenbull ran away because Shanks showed up at Wano, and that is only partially true, the fact is that after Shanks showed up, Greenbull's situation changed so that if he continued to go into Wano, he would have had to fight Luffy, Law, Kidd, and Shanks, Ben Beckman too if you think that he's above the normal strength of a yc1, and that situation is what Greenbull ran away from, not Shanks alone,