Madam Hooch role is described as Hogwarts' flying instructor.
Even though she does teach magic, she is not addressed as a professor.
I would imagine that, just like in the real world, to be called professor you would have to study yourself and have a degree, however, when Hagrid became the 'Care of Magical Creatures' teacher, he immediately received his title as a professor.
Even if technically students learn flying only for their first year, they still learn magic there, while on other classes, like 'Care of Magical Creatures' and 'History of Magic', they do not learn actual magic at all.
So why isn't Madam Hooch called professor while Hagrid is?