User blog comment:IamJakuhoRaikoben/Chapter 433 & 434: Ikusatsunagi & Demolition Fist, Review./@comment-25334245-20150518024529/@comment-7418318-20150604093935

The didn't say he was her grandfather, she just called him grandpa, but then almost all of Fairy Tail calls Makarov grandpa too, so that doesn't mean they actually are related.

And I can't imagine Arlock being Rusty Rose. Why would Rusty forgoe his super powerful Arc of Embodiment for those much weaker spells Arlock used?