Alternatively, you can look at the consistent styles in Mashima's former works (Rave Master, Monster Hunter Orage) and history (He and Oda were both Watsuki Nobuhiro's assistants), and make a more educated, fair and informed guess that he and Oda worked together and thus they have similar styles.
Still, I doubt Fairy Taild would have been any outstanding shonen if Eiichiro Oda didn't publish One Piece with similar style. I think we all agree Hiro Mashima owes Oda part of his popularity.