He could've pulled a number of things really. Told her they're childhood friends, that they're neighbors, they bumped into each other and she just happened to ask "hey could you do me a favor," etc. The whole chapter felt a bit forced, especially when the random girl came just to be condescending and leave.
Why do they call themselves "lovers" if they don't even hold hands? They are just step brother and step sister that live together and are kind of affectionate for each other...