「ほんなん」＝「そんなこと」/「そうなの」/「そうなんだ」
this vocab is a bit more unique has more of a variety in it’s usage, so the general sentiment is そんなこと but you can use it in sentences where it’ll turn into そうなの or そうなんだ
you can see in the example the the closest is そんなこと but even then it feels a bit different in use
Volume 1 Chapter 1
note that needs to be checked:
I feel like I’ve seen some media use it with a similar meaning to それじゃ but since I can’t pinpoint it I can’t confirm + media 関西弁 isn’t always accurate
