I am assuming there is no record of a major tsunami in Japan or China at this time, if for no other reason than it would get mentioned. Especially since there is a rather strained mention of a typhoon four years later..
That leaves us with coastal peoples in the Middle Pacific Islands and the Eastern Pacific coasts .. and New Zealand. I don't have that much problem with the idea of comet fragments explaining the cited events there; my problem is with the idea that this could've reached the scale required for global climate change.
You cannot alter the El Niño system, typhoon/monsoon patterns, and Eurasian temperatures without an extremely dramatic ground impact.
I agree with your disposition. However, I don't think we have the 'whole story' yet.