It wasn't strange to see an Atlantean and a mer together. They basically went hand in hand. However, it was strange to see a Wayne mer getting along with an Atlantean.
Ever since Bruce had a falling out with some Atlantean he dated, there has been a strict rule of not talking to Atlanteans. But of course, Jason would never follow the rules of his adoptive father.
Jason has always been the blobfish of the family. Whether it's for going behind Bruce's back and starting a rebellion, or for befriending an Atlantean despite the rules, it doesn't matter. He has always been a ruler breaker and a rebel.
It was unusual when an Atlantean found their way into Gotham Bay. No one knew how or why they ended up there, but they did. Bruce interrogated them, thinking they might be related to his old fling, but they weren't. They were sent on their way, and Jason decided to go with them.
They started talking on their way back, and they realized how alike they were. Jason decided that he would start visiting this Atlantean during his free time. They eventually became friends.
As they grew closer, Jason would spend days at a time with them. He would go to them after fights with Bruce or when he needed to decompress. They became close friends, and Jason wanted to take it further.
He realized after about the second week he stayed with them that he had a crush. A whole hearted crush. He would state longingly at them when they turned away. When he slept, he would dream of a life with them as his mate. Do Atlanteans mate? He's not sure.
He would start to bring little trinkets that reminded him of them and place them around their home. He wouldn't consider it courting, they were just friends after all, but he wasn't sure what else it could be.
"Hey, I brought some groceries and put them up since you were running low." He swam into their view. "Oh! And I bought this because it made me think of you." He pulled out a little ceramic seahorse from behind his back and presented it to them. "Please say you like it."