In one of his first posts he explained it “ Peepaw, so named by my 3 year old grandson. ”
In my experience, this is a common name given to grandfathers in the south. Beats the name given to grandmothers: memaw. Sounds like a donkey with a lisp.
Let the guy use it without any grief - it came from his grandson, for crying out loud!
Addendum: as I was drafting this, peepaw wrote a response of his own which renders this one pretty much moot.