They have been slowly building Roy's character, as he was known in the original comics, as Arrow's sidekick "Speedy", he also later went on to be known as "Arsenal", and later still "The Red Arrow".
He was a founder member of the group "The Outsiders", along with Nightwing.
As Arsenal, he was shot by Brother Blood, while attempting to stop him from activating a network of sleeper agents, and later upon clashing with Deathstroke, the scars from that shot, saved his life, when Deathstroke figured that he had suffered enough.
Eventually, Roy joined the Justice League at the behest of Hal Jordan, under the guise "Red Arrow", in homage to his 'father figure'.
So, while having super strength is a new idea, it is not as though the character isn't expected to develop into something more. Of course, Oliver does call Thea "Speedy", which makes things even more confusing.