so the grandpa instantly knocks out the dad with a single punch showing that he is far stronger than him yet later the dad is able to take down the grandpa with a single chop to the back?
Karma? What goes around come back to bite yah.
Give it a couple of chapters and it will be explained.
The dad snuck up from behind and hit his acupoint
People in wuxia manhua only become sharper the older they get.
I guess it’s supposed to fix the plothole or else he would have gone wild.