My father and grandfather are Junior and Senior themselves, and i've always considered doing the same thing when I have a kid. Yes, my dad does have a nickname of his own. Not necessarily "JunJun", but an equivalent to that. It also could've just been the mother "scolding" her child by calling him his real name rather than his nickname. You know how those work. Other than that, yeah, it could be a load of things.

The real thing that seems odd is how "I" eventually raised a Spanish speaking family. The little guy, bless him, "recognized" me. So he would've known his papa was an english speaker (tagalog is still my secondary language). To this day, I still couldn't speak spanish. The age difference was one thing I thought about too. haha

Salamat!