@Pringles
Non trolling answer :
Shanks reacted that way from using first sight and seeing Kid massacre his fleet, Luffy is reacting that way from sensing Kizaru’s power as a chapter ending cliffhanger.
Sure you can claim Luffy saw a vision of Kizaru massacring his weaker crewmates, but this is not how the chapter presents it. Based on what we have.
Non trolling answer :
Shanks reacted that way from using first sight and seeing Kid massacre his fleet, Luffy is reacting that way from sensing Kizaru’s power as a chapter ending cliffhanger.
Sure you can claim Luffy saw a vision of Kizaru massacring his weaker crewmates, but this is not how the chapter presents it. Based on what we have.