Remember in Maximum Capacity when Steven found that cage and said, "Seriously, when did you even have a cat!?"
And then in Ocean Gem where Greg saw Lion and said "Youuu?!"
What if...
Rose gave Greg a magical pet lion (obvoiusly Lion) before she "died" so he could take care of it. When Lion was little, he ran away. Greg hasn't seen him since and has just been taking care of Steven. When Greg saw him in Ocean Gem, he recognized him and remembered when he ran away and was surprised to see him.
Huh? Huuuuh?
I don't even know if anyone else has made the theory but...
Whatever!!!
:3